My puppy was pretty skeletal when I got her too...she was only at the rescue 4 days, and the Purina/Alpo mix they were feeding her didn't make much of a dent in that time.
My vet told me to just feed her a good food at the normal recommended amount 3x/day despite her already being ~4 months old, in order to help her stomach adjust to getting a decent amount of food. She was also getting lots of healthy treats (fruit, liver treats) to help her realize that people weren't scary. Between the food and treats she gradually added padding and growth.
Here's a website I found back then to back up what my vet told me:
http://www.thepetcenter.com/imtop/recovery.html
If possible, I would recommend recording her weight, as they recommend, both to assure yourself that she is actually gaining weight, and to have a record for your vet just in case.
Good luck with your new baby! She looks like a cutey!
EDIT: seconding what some others said above...you might want to try a high quality food like Canidae (normally the most economical high-end food) to optimize the nutrition she's getting from each meal and reduce the chances of a bad reaction to food. It's really not much more expensive than feeding a mid-grade food, but much much better for your dog
Sorry for the long post