Sorry, John, but there's a big difference between trying to create separation and being significantly negative so that you drop to 300+ feet and out of site with great rapidity. What I said that it didn't appear she was in any great hurry to create separation. If this happened over the course of a half minute or less, then the DM would have had to react quickly to recognize the situation and act. If it happened over 2-3 minutes of contact or more, there was a lot of opportunity for the light to go on and to initiate a rescue.
One clue is that the victim was "swimming" away. With suicidal intent, wouldn't you think the diver would enter the water a few pounds negative and use that to help with the descent? Down 100', the wetsuit should have lost some lift creating more negativity, but still she was swimming deeper. I don't know how many seconds or minutes this whole event took to go from 80' to 140'+, but it didn't sound like it was all that fast. In fact, the faster the victim was trying to escape into the deep, the more of a red flag it should have been for the DM/buddy that some action needed to be taken. It sounded more like a leisurely and deliberate descent that would elicit an attempt to communicate rather than a full-out rescue effort.