Welcome to YT and congrats on your first yorkie! You have a little chubby
If I were you, I would, over the next week, gradually change her food altogether. I think it is ok to free feed but it is important to feed a quality premium food with no fillers. They will probably eat less than something like Beneful. It is also important to find a food with no corn or byproducts. I use Natural Balance for Chewy but there are some fabulous premium foods, Canidae, Innova, Chicken Soup... I'm not a huge fan of Royal Canin because it has so much corn, but their kibble is small enoughh for the pups and it provides a good amount of fat. I started Chewy on this and then changed at maybe 5 months old.
Good luck and post pics!