I'm confused here, is she saying that she won't marry you until you cut your hair or she said yes she would marry you but would like for you to cut your hair. If she's saying that she's not going to marry you unless you cut your hair then that's sounds like control. I would defiantly call her on the carpet about that. And besides she accept you and love you for who you are even if you don't cut your hair, she loves you right.
She is trying to tell u that your shoulder length hair is not attractive on you. Listen to her advice. would u accept and love your better half if they gained 75 lbs??? or if they starte to not shower??? love is conditional. have u started slacking in " I'm gonna try and impress her" dept.???