I'm sorry you had to deal with her rudeness. Obviously, from your story, her intent was to be rude. Sometimes people just don't think, though, and maybe don't intend to offend others. Like maybe she didn't know enough about dogs to know that males tend to be larger or about her particular breed to know what the normal size range is. I know there was one time I was in Petsmart when I saw a lady with what I assumed was a chihuahua. I say assumed because this dog was the largest chihuahua I had ever seen in my life! This little guy was easily more than 3x the standard. I think my reaction was "oh wow! Is that a chihuahua?" I in no way meant any offense by this. I love all dogs and have a soft spot for chihuahuas as my mother had one when I was growing up. He was definitely one of the nicest little chihuahuas I have met. Then the lady pulled probably the tiniest chihuahua I had ever seen out of her coat. Even for a 5 month old puppy, this girl was tiny. She was super nice and pleased to show off both her babies and we probably stood there and spoke for close to an hour.
I think that, although the OP made it clear that this particular individual intended to be rude, sometimes we might think others are being rude or critical when maybe they're not trying to be. I don't think talking about size is always rude, even with human babies. I know it was routine for strangers to ask me how old my son was when he was a baby and they would often remark on how tall he was. I didn't take offense to it and don't when people remark about my dogs. I think a lot of people are just uninformed. If someone remarks how small my dogs are, I usually reply with the standard and comment about the wide variation and how big some can get. I don't always try to educate everyone that talks to me, but I try to be friendly and not take offense as much as possible.