Do you mean to tell me that being adorable doesn't burn calories?!
Good question on how much to reduce her food. Max was on restricted activity once for a week and I couldn't believe how fast he gained weight. He had a little pot belly. They lose weight fast too though.
I don't think there is one formula that will suit all dogs. If she is tolerating the reduction well and not showing significant weight gain in a week, I think you are on the right track.
Sending healing wishes to your sweet Zoey.