Its a bit weird to see Shadowheart surrounded by dead Intellect Devourers but I just assume they died by some other means, maybe a crash, since there are fisherfolk bodies scattered around as well. We are not shown that she fought them and she does not state so either, so...
Edit: fighting them later on yes, does suspend your disbelief, as a first level character you should be completely decimated.
It is implied in the dialogue with her that she did indeed kill them. Somehow. As a drow you can even compliment her on the carnage at her feet. And she thanks you even. So, I dunno, maybe aside from the wonder Gale we have another god's chosen at our disposal? At this point nothing will surprise me.
And yes, thank you for that edit. It's the point I've been trying to make.