I understand a little why she's being so defensive. She probably sees all the critique as criticism, and it outweighs the positive feedback to her.
But take what they're giving you and use it, Lady. It's pretty valuable stuff--they're noticing things that to most people make pictures look "off" without really knowing why.
Please don't get discouraged--you do improve very quickly, and the more you draw using the advice they give you, pretty soon you won't even have to think about proportions.
I can tell you a little trick regarding arm length, though: hanging loosely by the character's sides, the fingertips should reach a little above half the thigh. Once you've established this, you can have them in any pose you want, and they should be fine.
Don't know if that helped at all, but you know.
