How to say "get well" without sounding contrived?

At University a professor I am close to on a professional basis has been away on sick leave. I know that it is her partner who is very ill, but this is not something that has been announced.

Anyway, how can I wish her well without being specific? Would it be appropriate to send a Christmas card or something similar? I do not have her address and they will not be coming in to University any time soon.

I think it would be nice to say something just so she knows she is being thought of – or maybe I’m wrong.