You might have to cut her food back a bit more as well as doing low-fat treats. Poor Bella (a pint-size at 10kg but she was 12kg at one point) is on a raw diet but she only gets 140g of food a day, it really is practically nothing and I feel sorry for her but if she has more than that, she puts weight on. She gets a small chicken wing in the morning and literally 40g of mince (about a dessertspoonful) in the evening, and then low-fat treats.
And lots of running around as well but she just has a really slow metabolism, bless her...
We give things like cherry tomatoes, ends of carrots, apple etc and those dried fish skin cubes as they don't seem to be fattening for her (and they're good as a bigger treat).
For high value treats on walks/training she gets low-fat chicken frankfurters (the Herta ones) cut into teeny slices.
The night she has her agility class (tonight) she doesn't get any dinner as she gets lots of frankfurter.
My vet always says that if you cut their food by 15% they aren't really going to notice it, I think it's more us that feel the pang of guilt...