My girlfriend doesn't take compliments.. help?

So I'm coping with this problem almost every day... I compliment her about many things not just appearance gifts. But she really is BEAUTIFUL every common friend we have will tell me this and that im lucky and such things.. She won't believe she's pretty. And I believe what I say, I mean it. But she won't take them. What can I do to convince her.. to make her believe that I mean those words? I really mean them!!
My girlfriend doesn't take compliments.. help?
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