I was wondering the same thing, she was diving with her husband. Personally, I would watch out for my wife. I would not lose her
You are a fully formed adult human being diver used to diving self-reliant with all of the items you need to make the dive on your own. I happen to know this. You may be the common type of diver in the places you dive, but many (and no disrespect intended) are follow the leader vacation divers. At times, we (spree) would show up at the Dry Tortugas or Flower Gardens, 100 miles from nowhere, and some divers wanted to know who their leader would be.
Many divers expect there to be someone in the water to take care of them, because the major tourist destinations provide just such a person.
As has been discussed here ad nauseum, no one can take care of you in the water, and if you want someone to keep their eyes on you, you need to stay in front of them, but that certainly doesn't mean that they will keep their eyes on you 100% of the time.
It takes a split second to lose your team mate. I hesitate to use the term buddy as I think it's stupid, as it implies a standard of care that obviously wasn't followed in this case. I hate "leading" dives for the same reason, and especially on a 95 foot deep wreck in 150 feet of water where a diver could (and have) disappeared in the wreck, off the wreck, and on the surface in a smoking current. Last dive I led was on the white sand in a cove in pool-like conditions, and left that job for a better one.
I am not here to shame the DM or the husband or the victim. IRL divers expect someone to watch out for them. The reality is that all divers must be competent and self-reliant.