Did you mention any sort of increased anxiety, insomnia, or depression or some physical symptoms like fatigue that she thinks some exercise might help with? Or maybe she's talking about a moderate amount of activity improving the immune system (maybe relevant given recently getting sick) That'd be the most innocent explanation, anyways. Your therapist seems really odd though. Have you tried asking her to explain why she asks stuff like that when it comes across as out of place? I think it'd be easier for someone to give a real answer in the context of the whole session which she has (and of course she's the therapist who knows her own approach).