Bargaining from a strong position
As she mentioned, Giant Girl always tries reason first. If wading through the Goblin army and holding a mountain over the city doesn’t impress upon them that they should maybe rethink this war on humanity thing, she doesn’t really know what will.
Seeing the flayed captives being lit on fire and launched at her finally clinches that these are Bad People and offer her considerable justification.
The mother and child in Panel 7 will be seen on the next page, with a bit of a change of heart once they realize what’s coming.