One thing I know is when I was in a bad place I was not consistent, also I tended to be bad tempered, plus of course specific things or pressure made me worse.

If I was in your shoes I'd have to realize - as CJames has said - that you need to make sure you are OK long term. One of the ways of doing that is not to try to try to accommodate your freind's every mood change but simply try to steer a sensible constant course. If you can get across the idea that you are going to be there for her that is a very big thing. My partner did this and it made a world of difference to me. What I'm saying here is based on my experience with her.