Big mistake was letting HER pick the place for the second date and picking an expensive place and then you still paying for it without any pushback. What I would have said beforehand is, "wow you're taking me out to an expensive restaurant tonight? Awesome!" And see what see would've said before the date. She obviously wasn't planning on paying for it even though SHE picked the place and you already paid for the first date.
First date, man pays. Second date and dates thereafter, either the woman pays for her portion or even sometimes pays the whole bill. That's my rule of thumb. I'll treat them the first time, I'll take the lead, after that there needs to be reciprocation or at least an attempt.
First date whether it was cheap or expensive was on YOU. Second date ESPECIALLY when she picked the place AND it was a little pricey, she should have offered to at least pay for herself. But before that like I mentioned, I would've hinted that since she picked the place and it was expensive that it looks like she's treating YOU to a nice dinner!! If she would have said anything b*tchy or insisted that you were still paying for HER date idea, I obviously wouldn't have gone on the date and probably wouldn't want to see her again.
You already got sex after the first date and she probably figured you needed to pay for it through the nose afterwards by treating her to an expensive meal after having a cheaper first date that you also payed for. NEXT!!