Well, at first, it would be wise to ask her the reason why she doesn't wear glasses. She may not wear them if she felt that they were uncomfortable, or un cool. However, as a friend, we have to make her understand that it is important for her to wear her glasses. Her eye sight is poor, and so, it would only be the best for her if she wears glasses. Prevention is better than cure; if she doesn't wear glasses now, things can get difficult for herself. Therfore, she does the wrong thing for herself by choosing not to wear glasses. It may not look cool, but our well-being is much more important.
Hope this really helps you. ✌