Phknlwyr: Mrs. Law here. Brett ran into a similar "boat" last year. Brett had hired a new "boat" who, unfortunately, misrepresented herself on her resume. After about eight months, when Brett was missing court because she couldn't schedule, clients were getting arrested because she was not filing the proper documents and deadlines were being missed, it became clear that she didn't have a clue as to what she was doing (I don't understand why it took Brett that long, so don't ask!) The best part was that she had a plaque made for her desk which read "Legal Specialist". Anyway, one weekend, a friend of mine and I (we are both paralegals) went into Brett's office and went through all the files. We tried to do as much as we could to catch up, but some things we just had to leave notes on the files and leave them on her desk. Well, it was like the Leaning Tower of Pisa by the time it was all said and done.
The following Monday she comes into work to find all this crap on her desk and it was clear she was not impressed. When she left for lunch, Brett was trying to zip the vital files in her computer so she would not do anything to them. He, like you Phkn, got curious and started snooping around the history and e-mails. The history revealed that all she ever did at work was shop (she was overpaid) and her e-mails revealed a message to a friend about how much of a ***** I was to come into her work space and order her to do things, and who the hell did I think I was worrying about her job when I had my own job. (as if I wanted to spend my weekend doing her work) Brett printed the e-mail and when she got back from lunch he asked her to come into his office. She told him she couldn't right then, knowing that he would have to leave soon for Court. After she refused to speak with him, he came by my office on the way to court and brought me the e-mail. He didn't want to leave the situation the way it was and frankly, he just wanted her gone, but didn't have time to say "You're Fired". So, I marched my ass down there and very calmly told her that I knew she was upset about the work I had done over the weekend but that Brett was really disappointed in her performance and I went down the laundry list of things she had done incorrectly. She denied being upset and that is when I pulled out the e-mail. At which point I told her that Brett also didn't appreciate her using his time to write personal e-mails and to shop. Her jaw dropped and she was left speechless. I calmly told her that none of us should continue to suffer and that it was best for her to go.
If I were you, (or your wife) I could never let it go. Cuda is right, if I had not had the satisfaction of cutting the ropes on Brett's boat, then the frustration would have eaten me alive and Brett would have never heard the end of it. I think the best thing to do is just sit down with her on Friday and tell her how much you appreciate the hard work she did this week, but you don't appreciate the thing she wrote in the thread (and then hand it to her). She will be left a feeling of shame and guilt. If you do something really outrageous, you and your wife might be the ones feeling guilty and ashamed in a few months when the anger wears off.