How much was it for? The full $5000? If so, I'll blow your for $5K! OK. Maybe not. But I'd think about it!
Anyway, if it was a lesser amount, and I hope for your sake it was, it's probably gone unless you stop the check. As far as someone saying "they have laws" about checks, etc, well the laws protect you since it was pre-payment for a service not delivered. However, I doubt either of you will want to go to court over that.
I've loaned a few girls a few dollars over the years. I've always kept the amounts small. Enough they could easily repay with a visit or two (at most). Almost everyone has screwed me...and not in the way I wanted. But, like you, I gave it knowing it was probably gone. I use it to test the girls' integrity, or lack thereof. One was good about repaying me for a while, and then just went "south" in a hurry. Also, I would notice that I would have a girl that would post her rate at $200, but when she was desperate for the money, she'd see me at $150, but when I repayed her, her rate was $220 or $250. Things like that.
So, like Bubba said, chances are you're likely going to get burned giving money to a girl up front. Hopefully you're a quick learner. If not...well, I need some money for a surgery...I'll pay you back. I promise