Ouch, please help.

Hi guys! I'm new to the whole chinchilla thing. My girlfriend wanted one for a long time and finally convinced me to get one with her. I did the research and bought her a proper living area, food, toys ect. We went to PetSmart, now I regret going there. They had two females, one that was clearly an adult, and one that was maybe half her size.thinking it was a baby, or close to it we went with the smaller one. We talked to the employee and it seemed like she new what she was talking about. My girlfriend looked her over before we decided to take her home, she doesn't know much about healthy chinchillas. After giving her a little time to get use to her new home, I was cleaning out her cage and giving her fresh food. She started climbing all over my arm and running her head under my hand when I was trying to pick up some of the bedding. She was only here for a full day at this point, and I absolutely fell in love with her. She is the most friendly little girl and loves to play. As I was running my hand down her back I could feel all of her bones, her shoulders, and all of her ribs. I have never experienced petting a chinchilla before, but it honestly felt like she was nothing but bones under her fur.. they have a "return" policy there, but if this is the case where she is so under weight I couldn't ever, ever bring her back to a place like that. I saw the living conditions, they definitely were not ideal, nor was the care. I'm glad I brought her to a new home where she has room to run and play with people who love her. I just wanted to know if there was anything I can do to help? Should I bring her to the vet to have her looked over? I am buying a scale to weigh her properly. She appears to be young, with furry ears. I understand it's hard to judge it's age, and they don't ever know.

Thank you!