Feh. Let her be flippant and let her compete with you over hair (that is what she is doing). When she is being a b*tch about hair, smile sweetly and tell her her hair is just fine in a very reassuring way, as if she had said she was worried about it. It will make her paranoid lol. Her behavior and comments reveal plainly she is threatened by you, and that gorgeous waist length mane you have that I want someday!
The best revenge is better hair - eventually with all the pampering you are going to be doing, your hair is going to shine like the sun and be fabulous, I don't care how great her hair is, yours will look better because it's taken care of.
Plus, you have TLHC. Your length is enough to do all kinds of long hair styles and braids and updos that she can't do...so look around and start doing some. Get some awesome hairtoys, make your long hair your signature!