That's a really hard one. I don't think anyone likes to hear "you are not doing well" and many of us have heard it in ways that were painful, more than once. You might want to read the thread about one thing never to say to someone who is bipolar for some suggestions.

If it were me I sometimes am ready to hear that someone is worried about me and that I seem to be struggling (and I appreciate it being worded much like that) and sometimes I'm not. I am sure I give cues about how I feel and how open I am to that comment but I don't know what they are unless I am actually saying that I am not doing well in which case it's a good time to jump in with the I'm concerned thing. However I rarely will admit I'm not ok until someone else notices something, usually my therapist.

I become very paranoid about people's reactions and if they are going to try to scoop me up and dump me in a hospital. Which is why I don't like anyone saying something without taking cues from me or being too aggressive in what they say.

I think gaining her trust first is the priority. After that you can push a little more if you need to.