People have said things like this to me, also, and it stings.
I have a fairly good self-esteem, too, but one thing I am very self-conscious about is my back. I have scars from acne on my back, and I think it's ugly.
Once I asked my friend if it looked bad - we were about to go swimming, and my swimsuit showed it - and she said it looked horrible. I felt horrible after that. Once my friend's MOM told me I had an obnoxious laugh.
You aren't ugly, nobody is. And you may have great self-esteem, but you know the saying 'Sticks and stones may break my bones but words will never hurt me'? That's baloney. A better phrase would be 'Sticks and stones may break my bones but words are a freaking chainsaw'.
It's alright to feel upset, it's natural. I went through this very recently, even though I have a great self-esteem, also. Some people can be just downright rude.
And, judging by your simself xD, you are pretty. 'Sally' probably is envious of you, and is just trying to put you down. Yes, it's evil and it's cruel, but that's just the way some people are. So don't let her put you down - and maybe, try not to ask her opinion. I know this is hard, but I have a brutally honest friend and I've stopped asking her things because I always dread the answer.
So, in short, don't be discouraged. You are beautiful, and don't forget it. The only people that are truly ugly are the ones that call people ugly.