If she's chubby and has skin issues, I'd seriously consider having a bloodwork panel done to rule out thyroid problems.
Also, switching over to a higher-end food may help. Purina products have a lot of grains in them that some dogs have issues with. In the long run, a higher quality, more expensive food will cost you less because you'll need to feed less, and won't have to spend as much with vet visits.
