[Mayzoo]

Yeah, vet check first for any medical issues ie thyroid, liver, parasites, etc.... Also, the vet can give you an idea how much weight she may need to gain, how many calories to give her a day, and other general guidelines based on her size and health.

Then, supplement with treats like Yorkiemom1 says. Some say boiled chicken with white rice, cheerios or just other treats in general. She can earn them as you train with her too. Since you two just met, this would be good for bonding and setting up general rules and establishing polite behaviour.

You are right to keep the food available at all times like you have been. Some dogs can be free feed and not have weight issues, others cannot since they gain too much weight. Since yours is needing weight on, free feeding should be just fine.