Can Facebook Change people?

So my younger sister (16) got fb about a month ago snd she has completely changed. She got it secretly, I think because she didnt want me or my brother to add her as a friend or something. Anyway so I have been fb stalking her because she was being so secretive about it. I know I shouldnt but she never says anything and doesnt want anyone to know anything about her, which is weird because everyone else in my family is overly open about things. She doesnt seem to understand that just because I talk a lot that I still keep things to myself too. But on her fb she is always swearing on her status and things (in a positive way like "**** yeah!") which I think is really horrible. It feels like she is trying to be a different person. I know she is more like this with her friends at school but now she has become like that at home. She is always unusually super loud when she talks at dinner and then complains as soon as I speak that I'm shouting!!
I don't know why she is changing so much now because we have been getting on really well recently. It seems weird that it started after she got fb. Could this be what is making her so different?

Leave her alone, my cousin found me on facebook and is always going on about my photos or whatever to my aunts and it's none of her business

Facebook is very much about how you display yourself to other people.

Considering she's 16 she's probably just trying to fit in/look cool by swearing and such.

I only looked a few times and then left it.
I wouldn't have done it if she wasnt so secretive about it and I'm not going around talking about it all the time, I just want to know why she would be so different suddenly after getting fb.



Even so why would she be changing in person? Is she trying to make herself the person she is on facebook. And she never really had any problem talking to people or anything.

Just as a note, I'm two different people when I'm with family/friends.