Never Turn Your Back on a Hastings. Especially If They're Twins-- Jason and CeCe Twin Theory
Here are some clues:
--This started off by my friend, Mary, saying that she thinks CeCe is Mrs. D's daughter and that she believes CeCe threw the rock at Ali's head. Everyone's assuming it must have been one of Mrs. D's children who did this to Alison in order for Mrs. D to protect the person, and this would be a nice
alternative to the obvious choice, Jason. Jason also did say that he saw CeCe there that night.
--Jessica and CeCe look a LOT alike. If not for everything written online and the ABC Family hashtags etc, it almost looked like CECE was the one being buried at the end of the finale, that's how similar the two of them look.
--Mrs. D gave CeCe clothes; we learned this in the finale. It's possible that Mrs. D did this because CeCe is her daughter. We saw that she left notes for Ali with clothes in the finale; maybe she did similar gestures for CeCe. This COULD also have something to do with the similarities in their outfits on the night Ali disappeared. Either way, we know as a fact that CeCe had the shirt that Ashley Marin found in Alison's room that Mrs. D recently purchased. It is also possible, even if it's farfetched, that this has something to do with why CeCe was wearing such a similar outfit to Alison on the night she disappeared.
--It's possible that since Ali is younger than Jason and CeCe, that she wasn't told about CeCe being Jason's twin at all. Knowing Ali, she'd have figured it out somehow, but it still could explain why Mrs. DiLaurentis found their relationship so "toxic" and didn't want them spending time together. Maybe she was worried that CeCe would tell Ali the truth.
--CeCe could have had mental problems when she was young and might still have them to this day. One of the results is that she wants to be exactly like Alison; it's like she wants to BE her. She could be jealous because IF CeCe and Jason had any sort of violent childhood, maybe she was sent away to Radley. It could be a fraternal twin version of the story Ali told in "The First Secret." Maybe Jason didn't play with dolls, but something similar still could have happened.
--Speaking of "The First Secret," that's the episode where we first saw Ali's room. Most people are now aware that she has a sign in there in French about twins. It translates to "It's double the laughs, double the grins, & double the trouble if you're blessed with twins." Or at least it translates to something along those lines; I am going off memory. MY MAIN POINT ABOUT THE SIGN: everyone assumed this meant that Alison had a twin. If CeCe was Mrs. D's daughter and got sent to Radley at a young age, it's possible that the sign used to belong to CeCe. Maybe that used to even be CeCe's room, and that could explain why if Alison does NOT have a twin, she'd have a sign like that in her room. :)
--A big hole in this theory would be the fact that CeCe claims that Jason is her ex-boyfriend. We have seen NO FLASHBACKS of this supposed relationship. Instead, during the time CeCe supposedly dated Jason, we've seen her bar hopping with Ali and hooking up with numerous guys who were NOT Jason. However, the only times it was mentioned that CeCe dated Jason was when CeCe told the girls, and in that online series, "Pretty Dirty Secrets," when CeCe and Jason had a huge fight about their ex-relationship. That argument took place at the Costume shop and the ONLY person who heard it was Shana, so that could've been done purposely. The story that Jason and CeCe dated could be a cover story that they came up with when CeCe came back to Rosewood to explain how she knew the DiLaurentis family.
--Also (thanks again, Mary): When Spencer mentioned to Jason that she had met CeCe, Jason had an odd reaction. Spencer explained to Jason that CeCe told her that she had an "intense summer" with him. It was obvious that CeCe had told Spencer that she and Jason dated, but all he did was make a strange face and say "Everything about CeCe is intense." It seemed like there was something more to that intense story.
--CeCe being Jason's twin would explain why Peter Hastings is so involved with the night Ali disappeared, especially if CeCe IS the person who threw the rock. It could also explain some of the secret agreements and meetings between Peter and Jessica. If CeCe is Jason's twin, that means she's Peter's daughter too. This reminds me:
--When Spencer missed the UPenn early decision deadline, CeCe's word choice was VERY interesting. She said "You don't need early decision; YOU'RE A HASTINGS. IF I COULD GET IN, YOU COULD GET IN." Think about what that could possibly really mean. CeCe could be saying that she knows this firsthand because SHE'S a Hastings, Hence the "If I could get in, you could get in." That would be a very clever clue.
--Mrs. D and Peter could have been meeting because Mrs. D has been giving CeCe money secretly with Peter's help since she would be his daughter too. Jason could also be the person who was delivering money, clothing, etc to CeCe, and that could be the reason why Peter, Jessica and Jason lied about him being in rehab. Maybe they should've chosen a rehab facility that's actually still open and operating when they thought of this lie.
--IF "The First Secret" twin story that Ali told was based on any truth and CeCe was ever violent with Jason, that could be more indication that she is a violent person and maybe is the one who threw the rock at Ali. The story Ali told could have been loosely based on real life events in her family, even if Jason didn't play with dolls and bows.
--Maybe CeCe lied and it WAS her who pushed the girl down the stairs when she was kicked out of school. CeCe could have blamed Alison for this because she had issues and at times pretended to be Alison and they "switched personalities" according to Mrs. DiLaurentis. That would show MORE violence for CeCe.
--Depending on her mental issue level, maybe CeCe ACTUALLY believed some of her lies... Some people do that, make stories and actually believe them.. She could've told herself that Alison did some of the things she did, believed her own stories, and went to get revenge on Ali.
--Remember Noel's older brother, Eric? In the episode of PLL, "The Kahn Game," Spencer and Aria went with CeCe to a party at the Kahns' cabin. It was VERY clear that Eric knew CeCe, very well in the past. We now know, because of events in the season 4 finale, that Alison and Noel were VERY close as well and kept each others' secrets. CeCe's behavior before, during and after this party was odd. Before the party, she kept talking about her ex-relationship with Jason and how he wouldn't return any of her calls despite how long they dated.
--When they GOT to the party, CeCe acted like she barely remembered that Noel existed and that she didn't know who Jenna was. It became obvious that neither of those things were true, but CeCe could have been pretending to not remember those details so nobody would become suspicious of her for knowing too much about things that she wouldn't know if she was just some girl that Jason used to date. She wound up forgetting about her woes with her "relationship" with Jason and hooking up with Eric Kahn. CeCe becoming close with Eric Kahn could be ANOTHER way of her trying to be like Ali, since we now know how close Ali was with Noel. It makes sense that CeCe would try to become close with Noel's older brother in that case.
--The "CeCe is Jason's ex girlfriend" story is the PERFECT cover story for people who would never want anyone suspecting that they're related. CeCe saying she dated Jason stopped people from suspecting that she might be related to Ali and Jason.
--It doesn't make much sense why Mrs. DiLaurentis would pay CeCe to keep quiet about seeing Spencer with the shovel... Why would either one of them be willing to keep quiet for Spencer and Peter's benefit? If Peter knows about CeCe throwing the rock, under this theory, then it actually WOULD make sense. It seemed to me like there were some secrets that Jessica and Peter kept from one another despite their agreements. It didn't seem to me like Jessica knew that there was ever another girl buried after Alison, and I also didn't get the vibe that Peter knew that Jessica buried Alison. They could have made an agreement that what CeCe did would remain a secret as long as NOBODY ever knew about Spencer and that shovel. Peter DID know about the second girl and he DID think that Spencer was the person who killed her, so this would be a good reason for him to cooperate.
--In the PLL books, ALISON was the one related to the Hastings family AND the one with the twin.. Maybe in the show, those are going to BOTH be plot points for Jason; we already know one of them is.
--Supposedly CeCe visited Mona at Radley, and I believe this happened at least once. If CeCe is Jason's twin sister, her visits to Mona could tie into why Jason was later seen speaking to Mona.
I've listed a lot of clues so far, but let me know if you think of something that I didn't put in here! Thanks for reading!