With larger dogs the risk is great enough, but with the tiny dogs, the risk is SO much bigger! Please, do your
dog a favor and talk your mom out of wanting to breed her. Have your
dog spayed, and if your mom wants another puppy, buy her one either from a responsible breeder or adopt one for her from Yorkie rescue. There are more than enough Yorkies out there needing homes, you don't need to jeopardize your own little one to make more!