If she doesn't know that that's what you like about her, which would make her feel more secure, than it means she doesn't really like you. She doesn't consider herself "sexy" in your eyes, she doesn't consider your opinion highly which means that she doesn't consider you "sexy" If she's too wrapped in herself then she doesn't really see you, she only sees a temporary boyfriend replacement.
If you are seeing a particular girl, then you know why she finds you attractive, no? If you don't then you're screwed!!! You're setting yourself up to get hurt because you're emotionally investing in getting this girl's approval which appearently you don't have. Never assume that a girl likes you for who you are without adequate proof. People are with other people usually for selfish reasons/needs. If those selfish reasons/needs match yours, or somplement them, you have a happy long-term relationship.
You see when a girl sees a guy, she knows or assumes why he's with her based on her own self-worth evaluation. That means that if she finds herself not sexy, then she figures you're in it for the sex, so she's mentally counting you out. If she were sexy and you're seeing her, then she might figure you're with her because yu'd like to show off, and for sex, so she'll use that as tool. The only time this doesn't happen is if she's in love with you, in which case nothing else matters.
Anyway analyse the situation for yourself, and come up with your own explanation, jsut be careful and protect your heart.
Also careful with the C&F stuff because sometimes it has the opposite effect.