Why don't you ask her what's the problem
Hope there's no drugs involved
You may be right... Sounds like it..
Yes I hope not but sudden changes in mood and behaviour and paranoid could indicate drugs
I think you need to let her space of her own.
When we live with people, after some time their true character starts to show.
I think you should tell her about it.
Since you guys plan to live together its important to keep a healthy relationship. Maybe for you to be polite is something more important than for her.
Maybe there is something going on in her life. You should talk about it with her.