Religion & matters of the heart

Though you haven't mentioned it, I'm assuming that the fasting she does is the Ramadan ones and the basic five times salaats. There is nothing very religious about that. These are just basic requirements. If this is the case, I don't think she should compromise an inch on any of that.

If on the other hand, she was keeping nafl fasts all the time, spent hours in tahajjud and other nawafil salaat, and he's asking her to tone that down, then there might be room for compromise. But the way she's doing it, I think she's done the right thing and shouldn't even give it a second thought.