Friend issues? Urgent!!!?

okay so this girl is pretty much my best friend. we're super close and our families are really close too. i see her almost everyday at school and usually once on the weekends. lately i've noticed she acts kind of bipolar. one second she'll be texting me and she'll be nice, and then her texts will be unemotional and very stand offish, almost like she doesn't want to talk to me. and she doesn't reply to a lot of my texts either. it can get really annoying. she writes statuses like "things can't get any worse" "i need a miracle" and stuff like that, and i try my best to help her and i text her asking whats wrong and she doesn't answer. she just tells me her phone is dead, when i'm sure it's not. she texts her other friends like nothing is wrong, and then the next day she'll just text me as if nothing's wrong. and it upsets me because she changes her attitude towards me so often, even if i''m just trying to help her out. i feel like she always has excuses and all i'm really trying to do is help her in the long run, but she shuts me out. i don't know what to do??? i literally am starting to think shes bipolar...help?