whoa...that is sordid.... I don't know of a situation like that but as a female, the first thing I thought is that K is being loyal to J, and they have some relationship that is more than just friends...more than pimping even. For whatever reason, K wants to bond with J but have meaningless sex with men. Maybe she just wants to be nonsexual friends with J, but knows that J wants more so she's like stuck in this limbo b/c she doesn't want to lose her friend who she is close with...but she knows she will if she gets serious about a guy. So, she just is physical with guys and keeps her friend J.
If it were me. and I were K, I might have trust issues with men, maybe she's afraid she wont have a trusting, serious, committed bond with a man (if men have hurt her in the past). Dunno i'm totally 'projecting' as they say on the other boards. Good luck with your girl, it sounds like you really care for her.