Emotional Roller Coaster GF

My gf and I recently got into another fight after another one of her emotional break downs. I understand that humans aren't the most emotionally tuned creatures but I feel that she is a little over board. If I say something about another girl whether I say she is pretty, nice, cool, you name it, she gets depressed and self conscious. This also happens when I show any independence from her. If I show any sign of just wanting my own space for a while (ie not wanting to hold hands or be touching at all times). Every time this happens I'm expected to be the hero and make her feel good about herself. If not, then she goes around being depressed and saying depressing, demeaning things about herself. I know not everyone is perfect and loves everything about themselves 100% but am I supposed to be the key to her self worth? It's not like I don't tell her she is pretty or give her attention. I definitely do. The good kind if you know what I mean. However, no matter how much attention I gave her, sexual or not she still needs more to feel good about herself. What should I do/say? Is this normal? How do I help her?