Here is my 2cents for what it is worth. Food for thought anyway.

While I've never been in your exact situation, I did have a co-worker once who was having similar mental health problems to mine. She wanted to talk about it, and at one point, even tried to convince me to take a demotion, the way she did. She was genuinely trying to be helpful, but the way I looked at it, we just couldn't help each other. I don't think 1 drowning person can help another drowning person, you just end up pulling each other under.
So don't look at it as turning your back on her, necessarily. Really examine your relationship and be honest with yourself. Do you really believe you can help her or she can help you? If yes then fine, but if the answer is no, you need to accept that both of you need to look for help elsewhere. Definitely no "benefits".

Good luck to both of you :-)