We do not know if he fucked her or not.... we simply do not know what she would say to any of us if we just said "here's 10k, lets fuck". You would be surprised by how many girls that say "i would never fuck for money" would simply just say yes when they see that hot 10k cash pack in front of them....
This used to be an ongoing joke in my college with the girls in my classes until a dude found a fake stack of cash (10k in 100 euro bills) and replaced the top and bottom ones with real ones and was just asking girls to have sex with him, for fun, a lot of girls that were saying no prior to seeing the cash just said yes afterwards...
Given that Mary 100% does things in secret i highly doubt she wouldn't just fuck with him for cash and then just pretend it never happened for whatever reason, and given how delusional (and bipolar?) she is, she probably believed it too. (people forcing themselves to believe their own lies is a thing). In her mind she is always the victim in any situation ever.
And literally every girl in existence is a prostitute, you just have to find their price, some just fuck if you pay for dinner and drinks, others if you spend time with them, others with straight up cash in their pocket...It's a matter of perspective!