Oh yes, the problem is real. I must have heard the phrase "he's quite handsome, he's tall...", and the same applies to girls. Mothers seem to be sensitive to the matter. In fact this statements come often from MY mother chatting with other women. We also have a proverb that says "altezza, mezza bellezza", which means "height makes half beauty". Being average height, I realize the problem nevertheless.

Anyway, your mum should go to therapy, you just need to be proud of what your are (yeah, not easy at all, I know).

Let me tell you something: I practice a martial art named Aikido. If one wants to succeed at Aikido he'd better be small, because so he will need perfect tecniques, while big guys can rely on strenght, and their tecnique is poor. Aikido founder Morihei Ueshiba was 5 feet.
Actually, actor Steven Seagal is a supposed Aikido master. He is huge and he sucks indeed