No it doesn't, I didn't say that either. But accepting money for a blowjob does. When you catch her doing this, there are 3 options. One will have you talk sense into her, the other option will make her describe her pricing, including gangbangs, you can pay her $100 for a fuck. The 3rd option will have her say that this blowjob was the first time she did something like this, and the MC will consider hiring her for events. (It's possible I'm mixing up a few options in the dialog tree, but that's the gist of it.)
(NB: She won't do this if you're in a relationship with her.)
Right, with enough characterization, players can predict how someone will react given a situation. When Kari moves out and whores herself out to put money on the table, that's a decision that undermines the whole friendship with the MC. There's no lead-up to it, no way for the MC to prevent it (like offering her an actual job instead of an internship. He's been finding ways to provide for the most random of people, but not for a friend like her.)