It can be very frustrating dealing with people at times. I had a lady call my Gracie a BIG yorkie and she only weighed 5 3/4 lbs.
Anyway, I think that it is great that you are looking into making your baby a therapy dog. I've seen elderly people respond very well to these dogs.
I would totally disregard what people say about your dog. There is a lady that breeds her 13 lbs yorkie bitch and has beautiful pups that are about 5 lbs full grown. Instead of stooping to their level by making comments about their Biewers (which I am not saying that you have) just smile. If these breeders ask how much she weighs, tell them or not, it doesn't matter what they think. An 8 lb bitch will be able to carry her pups better than a 4 lbs one.