If someone dismisses a compliment, they are often seeking reassurance. Given that she seems to care about the compliments of others, I expect that she cares about compliments from you, even moreso, which could make her insecure.
GH: Nice hair... W: Need a haircut GH: Really? I think it is very becoming, it really frames your face in a way that I love.
GH: Nice shirt... W: It is old and stained. GH: Maybe so, but I love the way it brings out the color of your eyes.
Perhaps more specific compliments would help at the outset.
GH: I love your hair like that, it is so romantic I just want to carry you to the beach for a picnic under the stars.
GH: That color is great on you, the contrast really makes your eyes sparkle.
Such compliments are much more meaningful -- they seem more real and more sincere.
