Ok thanks. I didn't remember if all that had been laid out before. I don't like diving in a trio, and that explains why the men were paired and she went with the DM. Some suggest for newbies to buddy with the DM on lead dives but I don't like that either as the DM has to watch the entire group - whether at front spotting critters or on rear point.
We'll never know why Mrs.W took the plunge so we can leave that. It's somewhat understandable why the DM missed her descent having to oversee that flock. I believe the DM caught Mrs.W who fought off the DM? I know that some here have argued that if it had been them, they would have grabbed the valve and brought her up - period! I dunno? I've got my Rescue card but if a diver is intent on going somewhere, and I don't feel 100% sure that it's a save or let die thing that I can readily prove if challenged later, I might back off and see - especially if I'm taking a hard Narc, which I enjoy but they do fuddle minds. In a flashing thot I might also decide "Screw this! I'm all for saving someone who wants to be saved but not fighting suicidal lunatics at depth!" Maybe. I've had similar thots right before a car wreck: "That stupid @#*&! She cut right across me, this is all her fault, and I'm not rolling in the ditch to miss her!" I did brake hard, ruined two vehicles but no one was hurt.
So you and your wife had your vacation more than ruined witnessing a horrible, self inflicted death. Words fail me here so I'll go on. You stuck to your responsibility, your buddy, your wife, and that's great. I know you wish you could have helped but you couldn't. I can imagine the challenges trying to vacation or dive after that, do another trip, maybe even thinking clearly or sleeping well at times, or I can guess. I've seen people die but nothing like that.
Whether called Post-traumatic stress, or what Padi called it in the Rescue book, or whatever - it's important that you two accept assistance in dealing with having to witness that. I hope you have been in the last year and a half, but I think I see that you're still bothered so hope you are still talking this over with whomever - pastor, counselor, trusted friend, and will share more here if you want to. Prayer and meditation often help but I like spoken actions better myself. I've even seen some talk about fatal accidents at Open AA meetings I used to visit as a guest. I presume the speakers were drunks but it wasn't required at an Open meeting; they asked me to talk about whatever too.
Best wishes to you both. Hope diving is fun for y'all still. Whatever her problem was, she had no right to ruin any part of your life.