Ugh, some people.:grumpy: I'm glad she's back with you now!
Don't make her loose weight too quickly because it's really, really unhealthy for her and can cause serious liver problems. And it will make her body digest muscle tissue faster than fat tissue.
How long since you switched her to Manna Pro? I would give her a little time to adjust to eating that since it has aton less carbs than the Kaytee junk. If she's been on Manna Pro for maybe a week or so start cutting the pellets down to what you would feed her if she was the weight she's supposed to be. Maybe start with 1/2 cup pellets and unlimited grass hay, plus the larger cage, plenty of toys, and play time. Don't push her to run, etc. since her body might not be able to handle it. Keep her on this for a while and see how she does. Is sheloosing weight and/or developing more muscle mass? Depending on how weak her muscles are from the tiny cage she might bulk up with muscle before loosing much fat.
It might be a good idea to get a scale that can weigh her. A larger food scale or a baby scale might work, maybe someone has one you can borrow?
When she seems to not be loosing any more weight but is still overweight,start slowly reducing the pellets. Maybe to3/8 cup, then down to 1/4 cup.
It will take a long time for her to loose weight safely, but it will be worth it.