Well I wonder what her intent was by saying this to you. Does it make her feel superior in some way? Is she slighting you by this remark? How rude of a statement to critique a small child's teeth for pete's sake. I don't blame you for this comment getting your dander up. I'd feel the same way.
Advice to just ignore the remark is smart, but that's easier said than done. It was a hurtful comment. Some of us who are not of that persuasion, to be hurtful right back, or have a quick comeback for a remark like this, take things to heart. I would put this comment in my memory bank for safe storage and if another situation arises tell her to mind her own business and if she doesn't have anything nice to say, don't say it!!!
Some people always have to be the "smart" one, but that's a whole 'nother thread.
Flowers are nature's way of laughing