Too bad there isn't something in the text about Mab: and now that I think about it Titania, being shorter than the average fae, because then I think you might have something. However, that might not be a real clue either because I believe Mab can be any height she wants to be. I do remember that Lea is taller than Mab, though I can't remember what book I read that in.
If Mab = anyone else, I have to go with Ms. Duck's theory of Mab = Molly, though I don't really buy that one either.