My mom was not nasty or told bad things in a constant way. It was subtle. She was negative in the sense that she was unable to be hopeful. Regularly she expected things would get ugly at some point. She said she was realistic.
If you can, try to make an extra effort to trust your gut and not to give much authority to anybody including your mom. There is not any other authoritative voice about you than yourself. You are the expert on yourself. You have said you have self confidence issues and I bet this is something that goes beyond school bullying. I do not know you but I kindly ask you to consider that maybe your family dynamics have something to do with it. Not to hate them but to understand yourself deeply. To me there is not an objective and univocal criterion to define beauty in a person. But if there were a criterion, what your mom told you is not helpful, at least. You do not need to pay tribute to what she said because it is wrong coming from a mom. I worked as a school advisor for 14 years and when I heard comments like that from parents of students it was a red flag to me. Parents do not tell their children they are below pretty, or below normal intelligence, ever, and particularly if they are depressed. You do not need to pay attention to my comment, either but I really feel to tell you consider this a bit. Of course, I can be wrong and this is not my business and I am not being prudent here.
I know my mom loved me and I bet your mom loves you, too. But human beings are complicated.