And your wife has said they didn't do anything other than talk?
Did your proof of pictures or texts indicate anything other than talking.
Have her write out the timeline from start to finish. And have her do it quickly, a WS can take years to do that. Give her a deadline of a week or something, but not too long.
After that or if she refuses, have her take a polygraph. At the first mention of that, she could start talking more truths.
Have she read any books about affairs like Not Just Friends.
Does she even admit she did something wrong? Is she even sorry?