My best friend is flirting with a guy who has 1 thing on his mind, and its not her feelings.?

She'e been depressed because no guys ever really notice her, so its natural when a guy notices her she falls for him. Just yesterday she let him kiss her cheek (she's only known him personally for 3 days) and trap her n a corner of a pool and started "tickling" her. I tried telling her that she shouldnt let him do it cuz he's not after getting in her heart and she says she doesnt really like it but she lets him do it anyway. Help?