Seraphina could have hunted the trolls one by one with the full party. It would have been time-consuming, yes, but the risk of injuries could have been significantly reduced. Not to mention, their teamwork would have reduced the individual effort required from each member, as well as their mana consumption.
She still ordered the party to split up and attack the three different locations simultaneously because of a possibility she hadn't overlooked.
Since all the trolls were surrounding this part of the forest, each stationed almost equidistant from its neighbouring troll, what if a fight at one location alerted the other trolls as well? Or, even worse, the high-ranked monsters deeper within the forest?
If that happened, they would be swarmed by these high-ranked monsters.
Splitting the team certainly reduced their overall strength, but it eliminated the possibility of being surrounded from all sides.
