Perhaps its an age situation? When I was in my teens and 20s, people did comment on hair, and make comments similar to your friend's, ie., "I want to see what you'd look like if I straightened your hair, you'd be so pretty" - which is very rude, but your friend is oblivious to how rude that actually is to say to someone. If you turned around
and said, "I want to see what you looked like with your rude mouth taped shut" she'd probably gape at you cluelessly.
But in your 30s and 40s, I don't think people will say things like that to you. Not as much of a consolation I know, because hearing something like that is hurtful. You can
say something back, you know, and let her know you find that hurtful to hear, and that if she's a friend, she won't make comments that are insulting to you and hurtful about your appearance. Ask her if she'd like you to dissect her appearance in the same way.
I used to get comments in my teens and 20s that I don't get now that I'm the ripe old age of 40
Of course, now I have little grey curls popping up here and there. Not sure which I hate more...