Not sure what to do about my girlfriend's insecurities?

Anonymous
My girlfriend has had her friends and family including her mom saying I'm too good for her. But I don't think so. I really care about her but she constantly acts or says stuff that's harmful to herself mostly because so many people besides me put her down or said stuff like that. How can I help her feel better? Or more confident? I try to tell that I think she's beautiful and great but she just says I'm lying to make her feel better. And at this point I just don't know what to do.
Not sure what to do about my girlfriend's insecurities?
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