How did the game manage to instantly kill 3 of your party members?! (Judging by the screenshots, they were not just downed, but had been killed.)

To put in a different way (no offense), what did you do or not do such that 3 of your party members got killed like that? It was not like running into an unexpected ambush. If Shadowheart could single-handedly eliminate all the threats, why would 3 party members have to be dead? They could have just waited for Shadowheart to get her "job" done.