IMO, if she was not a pro, and was a sincere, authentic newcomer sb, you blew it by speaking to her in hooker/john language.
Half up front and showing her the other half was there is reasonable. I've heard of girls who have seemingly hit it off really good with a guy , they have sex then he acts indignant having to pay, thinking they had 'something special'. LOTS of scammers like that preying on less than savvy girls.
Agree to to the 50/50 online/text and see what kind of vibe you get from her in person. Then decide if she is going to have to go tend to a "family emergency' or otherwise have any idea she is going to flake otu. I doubt that if she has gone that far to have met , talked, meet and greet, social time and then be in your bedroom with a positive vibe, she's going to run off with $200 if there is $400 available for having some fun, with the possibility of a future.
Be aware, but don't treat them as professional working girls until such time as they make it clear they are... or you get authentic clues she is is. Even then, sometimes it's best to let them play out being a good girl gone bad for a night.
I'm pretty good at reading scammers so that's just my opinion.