Tough one, and I have this particular T shirt.
From my own perspective, 'went out' with a WG, got laid without paying. I knew she was a WG, had paid her previously
Things developed, and I was happy to live with a EX WG and she was happy to live with an EX punter.
First Question,would you be happy waking up next to her each morning.
A punt and a relationship are two totally different things, and you cant mix them, although you can make the transition if that what you BOTH want. if she had even mentioned me paying after that first time as more traditional date I would have headed for the hills.
My own advice, nothing venture, nothing have, but set some very clear lines in your own mind, and if these lines are crossed then run, fast, dont get dragged down. I think you need to have a 'talk' if things do look like they are going to be more than punter - pro, if shes interested she will listen and contribute, ask her what she wants out of a possible relationship, if you are on the same wavelength good, if not then youve dodged a bullet, move on before it gets awkward.
I couldn't be in a relationship with someone who is currently working as a pro. But other views exist and I would never judge.