Your wife may be fearful there is more than the chat site. Volunteer to change cellphones with her. Make sure she has access to all cellphone records (including work related). Volunteer to install a GPS tracking device on the car so she knows that you really are where you say you will/have been.
Why is she reluctant to go to counseling or examine the workings of the marriage? Is she fearful she'll come out looking like the bad guy? Does she fear she's been a bad wife? Does she fear telling you how hurt and angry she really is over your behavior? Does she fear honesty will drive you away?
She asked me to change my cell phone number so the OW can't get in touch with me and I agreed instantly to that. I have no problem letting her see whatever she wants, whenever she wants. She pays all of our bills, so she has always seen everything on our credit card statements and all.
I think part of the reason she is willing to push it away is that she knows deep inside that I never met this person. I am literally either with her and the kids, or home with the kids while she is out doing something or at work. I never leave early for work or come home late, and due to the nature of my job, she knows I can't leave work during the day. I think she really believes I never met this OW, which she should. I had even told the OW right at the beginning that meeting wasn't going to happen.
I am not sure why she was reluctant to go to counseling before now. I think BOTH of us are afraid to be honest with each other quite frankly. I don't think she is as honest with me about what she wants/needs as she should be and I feel the same way about myself. I am really looking forward to the counseling.
As for her getting on this website, I doubt it. I am an admin at a gaming website and we have a bunch of friends that we have met all over the country. She really likes these people a lot, but I can't get her online to keep in touch with them via the forums. There is also a local "moms" forum that I suggested she try to make some friends since we are still relatively new to our area. I thought it would be perfect for her to be able to exchange with people just like her. She just isn't "into it."

Thanks for all the really great advice turtlehead. I did some reading on this website yesterday and saw all of what you are talking about with the ENs. I really hope our counselor uses this same type of info.