I disagree, and have said so previously on here. If you are shooting yourself in the forehead with a full-sized service pistol then the hold she was using would be by far the most comfortable and easiest to use. Check the linked video from the scene in Lethal Weapon where Martin Riggs is contemplating shooting himself - he's using
precisely the hold that Jennifer used! Try to do, or at least think through, the physical contortions you'd need to use to get a conventional hold on the gun so that your trigger finger were actually on the trigger.
The study into where guns fell is an interesting one. I'll bet though that very few of those suicides involved shots to the forehead. I haven't read it all but if you were to isolate the incidents which were forehead shots which used this style of hold then I think that the number of instances in which the gun was retained in the hand would be far, far higher as it would be a very secure hold, I think. You have your fingers around the backstrap rather than your palm against it and fingers are designed for doing the job of exerting force! Your entire hand would be tensed. I'd guess that it would be actually uncommon for a gun such as this to fall away, quite honestly. That is also backed up by the fact that her thumb was still exerting pressure on the trigger when the gun was removed from her hand.