As an overweight teenager in the 1970's, when it wasn't as prevalent as it is today, I also wore braces and glasses. I will leave it to your imagination as to the amount of ridicule that I endured.
My mother didn't help much because she had suffered with an inferiority complex her entire life. What did help me was reading a book called "The Power of Positive Thinking", by Dr. Norman Vincent Peale. It is an old book now, so I will just give the part that I latched on to.
Dr. Peale described himself in college as having such an inferiority complex, that whenever the professor called on him in class, he stammered and stuttered and couldn't get the words out, even though he knew the answer. One day, the professor asked him to stay after class and addressed the situation. He told Peale that he knew that Peale knew the answers, and asked him why he couldn't speak up in class. As I recall the story, the professor really didn't wait for Dr. Peale to answer. He just gave him a good talking to and told him not to be so self-involved that he thought everyone was ridiculing him. He told Peale that most people really don't have time to pay so much attention to what other people were doing, and to remember that we are all equal when we come into this world, and we are really all the same.
Now, all of this didn't work immediately for me because I was in the seventh grade when I read the book, but it took hold, and I realized over time that there are always going to be people who look around and try to belittle others. This is unfortunate, but the thing to remember is that the type of person who does this is more insecure than the person that they are ridiculing. The trick is to develop the confidence in oneself to the point that when others try to ridicule or belittle us, we can see it for what it is and move forward. The most important thing to remember is that the opinion that matters the most about who we are is our own opinion.
Developing self-esteem will come with development of gifts and abilities, so that will also help a teenaged girl who is feeling insecure. It is also important not to admire the actresses and models for their skinny body styles and to emphasize that we all come in different shapes and sizes, but the most important aspect of a person is not on the outside.