I've found that comparing issues or problems never goes anywhere. People have problems that affect them, and that's all there is to it. Your anxiety and depression are severe enough that you sought therapy. They affect the quality of your life just as her cancer will hers.

I don't want to seem to be trivializing her disease, though you don't know how that will turn out - what the prognosis is, etc. But if she still wants to work with clients, she thinks your problems are important, too.