She looks like a really sweet girl. I am assuming the rescue org did some grooming for her to look nice to be adopted, because she looks well maintained in the pic. Chip was really skinny when he was adopted from Petfinder.com, he was under 10lbs at the time and now weighs 15lbs. When he was living with my sister I think he weighed even more than 15 lbs
Anyway, try some homecooked food the dogs really seem to like it more and will eat more of it. If you don't have time for homecooked, buy a rotisserie chicken from the market peel off the skin and mix the meat with some rice or potatoe.