The only thing you really can do is explain what's going on with you so she a) can try to understand, and b) hopefully modify her behaviour, or c) leave you alone for a bit. Friends talk about what's going on and if she's unaware, or unaware of the extent of it, she'll be unable to help or respond appropriately.
I certainly wouldn't ask her to tone down her happiness or otherwise change who she is, but maybe you need some space. It also sounds like you need some one-on-one counselling, hon. You're not in a good place and that can be resolved, either by understanding what's going on and why, and learning what to do about it, and/or by changing your mindset.
I'm not a counsellor, but you don't sound happy and you deserve to be.