Not sure if I should be putting in my two cents here. I am one of the great unwashed masses who can't get our wives to try it. I have asked however. lol. And I have been chatting with people who have tried it for a long time.
I am assuming she is willing to do it. I'll warn you that there are a lot of pretenders on the net. May take a while to find a real opponent. One short cut would be to join Voice Verified in the yahoo groups. Two benefits there: first the people have been prescreened (not a 100% guarantee, but better odds than any place else), and second you can check with their other opponents to make sure they are trustworthy.
Regardless where you find them, voice verify them yourself. Internet voice chat is fine, phone chat is better, Cam verification is best of all. Given that the cams and mics are cheap and pretty much everywhere they should be able to do that with you. If they can't, they probably either are not real or not very committed to finding opponents. Either way, they are probably wasting your time.
Once you are ready to meet, arrange to meet them somewhere public first. Enjoy a nice dinner or drink with them or at least meet in a public place. This gives you a chance to really get to know them, see their body language, make sure you are comfortable with them. If you are getting bad vibes do not ignore them. There will be other chances. If you have to travel, try to go someplace that will be fun for you even if they don't show. At least then it is not a total loss. Hopefully you can find somebody local as it will be easier.
If you are comfortable, have the match. Especially for the first couple matches I'd strongly recommend doing submission wrestling. Pin wrestling is fine, but hard to objectively call pins. Do as many falls as you want (best 2 of 3, 3 of 5, etc). The chances for injury in submission wrestling are extremely low. Strained muscles and maybe bruises are about the worst you can get as long as you follow the rules. It is a contact sport so there is always some risk but that is mostly at higher levels (I knew a wrestler in college that broke his pelvis wrestling, but that was when his opponent flipped him over and slammed him on the ground in near splits... not likely for most women unless they are superwoman). For extra safety, have the ladies start from the knees. Ideally, invest in a wrestling mat or pad. Carpet is fine, but it can leave burns and has surprisingly little cushion.
Then follow the rules. These things have a way of escalating, so be prepared to step in and stop it even if it is your gf who is escalating them. The goal is to have some sexy fun, not spend the night in jail for Assault.
Finally, be prepared to loose. It is important that you prepare her mentally for this, but also prepare yourself. So many of us guys get wrapped up in the winning or loosing. She has to know that you love her no matter what and you are proud of her no matter what. Remember 99.9% of us are not as lucky as you. She is doing this for you. You treat her right after or quite honestly you don't deserve her. She is your goddess!!! Treat her like one!