How do you tell a girl that she's beautiful when she doesn't believe it?

HAHAHAHHHAAA that's so funny. um, just be really cute in how you say it and tell her a lot, you could get her flowers or bursh some hair off of her face and look in her eyes. saying it over and over is key, but its really sweet and shell realize you mean it eventually, good luck! :)

You can't really tell her if she doesn't believe.

Seeing is believing. Show her how much you mean it by spending time with her, and constantly remind her how beautiful she is.

If she says "oh, this girl is pretty" etc.. tell her NO, she is the only one who is the prettiest, no other girl is prettier.

Hope I helped, good luck!

Keep on telling her consistently.

If you stop she'll wonder why your not telling her that anymore. She's just messing around not believing you because your teasing and she doesn't trust you.

stop laughing uncontrollably when you say it.

you write it down for her

YOU ARE BEAUTIFUL!