Friend has mental problems...

My friend has depression, anxiety, bipolar and a few other things. I try my hardest to accommodate for her, make sure she's comfortable in the right situations and I always invite her out to see each other.

My issue is, that it's becoming hard for me to cater for her. I feel helpless when she has her attacks and they're very frequent, so much so that most of our time together is her breaking down in one way or the other. Its a shame because she gets really excited to do things but can't do them last minute, this has made me lose money because ofcourse I wouldn't do something without her, I'll always go with her and make her feel better.

I'm becoming stressed, strained and exhausted. I don't know how I can keep up with her, I want to, but it's just getting so hard. What do I do?? I need help. I don't have mental issues myself, I understand hers but I'm just at my wits end