I think it's fine to have warm feelings towards your therapist.
Her marriage is besides the point--the fact that you guys have a therapist/client relationship is the boundary that can never be crossed.
But it might be useful to think about...what is it about her that you find so appealing? This can be a clue about what might be missing from your other relationships and other parts of your life. Then you can use that info to help you find that in the real world, in relationships that aren't out of bounds.