We have made is VERY clear to everyone who comes to our house or that we visit that Tia is to have NO TABLE SCRAPS. We're actually doing everything we can not to further encourage her existing LP (and our vet said that she must NOT become obese).....so we stretch the truth with our friends and family and say that it's for medical reasons. We hate it when dogs beg at the table and cruise around the kitchen. It's not to say that people food is bad....as long as it's not prepared people food. I give Tia baby carrots, cheese and will try to see if she likes yoghurt, but it's given as a treat, or in her dog dish...not from our hands when we are sitting at the table.
In response to your post (and I'm just making an assumption here), you seem to be more concerned with the fact that someone broke your "rule", rather than what your puppy ate (unless you're worried about chicken bones, which are really bad!). Just be honest and candid with your mom and try to make her understand WHY you have certain rules with your pup. And if your mom can't follow the rules...then she could get her own Yorkie to spoil
They could be cousins!