Her backtracking is shown in the two first pages of Chapter 18. I think consensus is that she mistook the situation for a mutual kill. She doesn't know what Finnish magic is capable of (Lalli is her first Finnish mage), but Emil did have explosives with him. "Eaten" is also only one of the possibilities she considers. The "crushed" and "drowned" options are hardly incompatible with blowing up something that big, without being careful, near a large body of water.