She's probably waiting for you to bring it up, otherwise she would be imposing her issue upon you. If you bring it up, she may want to explore your feelings about her health. But I think it's important to do so because it's understandably concerning you.

My T's health has been up and down since near the end of my therapy, and was the reason for his retirement. He knows I carry a concern for him, so he's always been very straightforward with me about his health. I appreciate that.