My little Amber is up to 12 pounds because of steroids and I do NOT free feed. Sometimes it just happens.

Has she has bloodwork done at all? It may be an imbalance as well as too many treats. If she gains weight on light food, I'd be suspicious.

What type of toy does she like? A feather or tinsel teaser wand is usually great! When she begs for treats try to get her interested in the toy for a while. And if you must give her treats, giver her just ONE.