It might be tough . Sometimes a poor self image and lack of confidence has been driven into a person since childhood, with mental and or physical abuse. She's going to have to overcome it herself and about all you can do is to be there as her friend and support her as best you can.

let me be frank: her opinion of herself is not the same as the one you think she has. What she really thinks is how much she loves to be told (by you, repeatedly), what a super person she is and how great she is. She does not think that she's horrible in the least - she thinks she's not only great, but also better than you, by a long shot. That's why she keeps making you tell her again and again, (...'you are a pretty girl, look in the mirror and see how pretty you are, and then she does). Bet she never tells you what a great friend you are. Bet she never says that you are really pretty and all the boys seem to like you. Of course she doesn't. For her to shine she require 100% of the attention on her, not you. And you, so far are doing this brilliantly. I'm sorry to be brutal but this is what is happening. It is why she never believes the compliments you pay to her. She can't can she, if she did, you would stop saying them over and over. Personnally, I think that you sound like a kind natured person, somebody who is loyal and is prepared to put somebody else above themselves (even if you do it in detriment to yourself). You appear to be the kind of person one would choose to have as a friend. Trusting and loving. Good natured and kind, decent and honest and of a caring disposition. And all of these admirable qualities that you possess are the very reason that she does not want you to have any attention - because if you do, you will outshine her quite naturally - others will gravitate to you, not her. And she knows it. With respect, I'm guessing that you are young and not so experienced yet - remember, a friendship between 2 people must be 50/50 - both are equal to other, neither is better than the other, each looks after the other and does things which may the other happy. I think you deserve a better friend. I'd pick you as a friend, any day of the week just based on this question. You seem to have some of the qualities that I look for. Now, she should be telling you this, not me.

CardShark made some good points imo.You could suggest to your friend gently that she might benefit from seeing a counsellor e.g at school,college,or outside of this, (thses counsellors are often trained to help people who have self esteem issues).

A lot of people have trouble appreciating themselves, and may be harshly judgmental of themselves. The causes can be somewhat complicated. The best thing I can recommend to you is to help her develop some self-awareness: don't try to convince her that she's wonderful, or that she's wrong for believing what she believes. Instead, point out to her that she's having certain "automated" thoughts which she always has. These thoughts are like a tape recorder on a loop: it just plays the same song over and over again, regardless of who's in the room. If you try to make her "think positively", what you're really doing is injecting ANOTHER tape recorder (playing a "positive" loop). Now its even noisier than before inside her head. While sometimes the "positive" tape recorder can drown out the "negative" tape recorder, none of these tape loops actually help a person understand themselves any better, or resolve the core issues of self-doubt, fear, and rigid judgmentalness. So awareness is the key: the more she can be aware of her own thoughts and feelings, without having to run away from them, the more she'll be able to develop a more balanced view of who she is, what her abilities and strengths are, as well as what her weaknesses are. That's the road to health for all of us.

Teenagers being alienated from parents and all that stuff is totally normally - it happens when you grow up. That is life. Moody, sulky, insecure, mouthy teenagers are like that. They also think they know everything when they don't. And we are all like it at some stage. I daresay that my son will be a typical teenager and just as difficult as the rest of them. So, taking into account your background, why did you not offer any appropriate advice?