Maybe the arrows don't kill that elf (only knocks her out) and she becomes important in a later battle as she tries to avenge the princess's death or something like that. I don't know if your orc would hold a grudge against her or not for killing his hand picked orcs.
Btw the tremor and dust and stuff is one of the elephants slamming its tusks onnto the ground/ area they are at, one of them seperating Kotagnac and Velice, while the second tusk is behind Kotagnac.