Is something mentally wrong with my friend?

I have a really good friend of mine who has recently been acting completely out whack. Her and I are members of the Global Issues club at school an we’re both really committed to creating positive change in the world. She didn’t show up for the last meeting. She’s also a straight A student who is really quiet. She’s been talking back to the teachers and refusing to hand in her homework recently.
During lunch she would spend an hour staring at the wall and laughing periodically for absolutely no reason. When I would ask her what was wrong she would say “All of you don’t get it.. You wont ever get it”. She also goes on and on about how Hamlet (the play written by Shakespeare) has changed her life. She says she gone through a sudden epiphany of sorts. She isnt herself at all! She’s even talking about to teachers and laughing out loud in class during moments of complete silence. Her mother said she was doing all of this stuff at home too. I am really worried about her. What could be wrong?