I think my crush has low self esteem?

So my friend Amy is awesome. She nice and smart and gets super good grades. She's a people person and everyone I know like her. She can make anyone laugh and he's great.
Today I told her she was pretty an he replied with "don't day that, I'm not pretty". She had the most serious look I've ever seen. It was almost scary hearing how serious her voice was. But I dot get it, she's dresses really nice everyday (won superlative for best dressed). She's not fat, in fact she's really curvy with a nice bum and big boobs. and she takes care of herself but she doesn't think she's pretty. I just don't know what's up with that. Also how can I make her realize she's cute
I think my crush has low self esteem?
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