Assessing people’s coachability

Do you have advice, or a sort of litmus test, to decide if someone will be coachable by you or not?
I imagine you have developed a strong gut feeling by now, but what about us coaches with less experience?

Someone has approached me and is interested in my coaching services. She has multiple sclerosis and has many negative thoughts about the illness and how it affects her life prospects and her relationships.

I can see how her thoughts are creating a thick layer of emotional suffering, and I know I can help her untangle them so she can better deal with the physical aspects of her illness, but I think she has a long way to go. From my early exchanges with her, she doesn’t seem ready to hear that her MS is a neutral circumstance, and although I’ve introduced her to the concept of changing your thoughts to change your feelings, I think it will take a few sessions for her to see how it really works and what the end game is — if she’ll let me.

I haven’t yet coached anyone with this kind of mindset. Should I see this as an amazing challenge for us both, and a coaching relationship in which I can really make a difference? Or, if I’m not 100% confident I can deliver life-changing results (because it’s a very new coaching situation for me), I should opt out? What happens when it turns out the person asking to be coached is not ready to be coached after all?

I think I’m answering my own question as I type this (= help her the best way I know how) but would appreciate your insights. Thank you!