How to help a truly insecure friend

How does one really help a truly insecure friend? She honestly thinks she's extremely unattractive. She gets in these moods where she thinks she's not good enough, no guy wants her etc... then gets upset when me and our other friend tries to talk to her about it and explaining to her that if she truly feels that way then she needs to take those things that makes her feel unattractive and work on it, (ex. She thinks she's fat, or doesn't like her hair, etc..) but she just gets upset with us and claims we don't know what it's like and we get hit on all the time (which isn't true at all) and that we'be never experienced this. It just makes me so irritated bc I've been where she is when I was younger but I worked on this things until I started feeling more confident in myself, and it's like I want to help her but at the same time she doesn't even want to help herself...