If you think about it, she had to interact with this guy a bunch of times. It wasn't ONE moment of weakness. It was a series of decisions. First, she was interacting with him in such a way that he felt she'd be open to selling nudes, probably multiple interactions with sexual overtones and flirting. I know women get DMs all the time with creepy stuff, but I don't think guys usually open by asking "Do you SELL nudes?" They're usually looking for freebie stuff. Then she had to pose for and take the pictures, review them to see if liked them enough to send, and maybe the pictures were even taken according to some specification the guy had (how she was posing, what parts specifically were showing, etc). So that probably took awhile. Then she had to arrange pricing and payment details. Then she probably had followed-up communication with the guy where he told her how much he liked her pictures and she thanked him and whatever.

Now, if she had done all that, taken all these steps toward ensuring this guy got her nudes, just because she wanted to and not for money, would you think it's a bigger deal or a lesser deal? Does the fact that she did it for money make it "not as cheat-y" somehow, or does it make it even worse, like she's easily able to compromise her morals if she can profit from it?