What I think has happened is that Firehelm's actions have saddled her with a responsibility she can't shirk when she feels like it and that pisses her off. If it's one thing she hates its being responsible. I mean, the Giant could totally botch the handling (he's human after all), and make Durkon the bad guy for not being there for a child he had no idea existed at all. It wasn't as if she was breaking her back or bank account to scry him or do a sending, which she probably can do being a cleric. This is an event with zero foreshadowing, and adding a bunch after the fact would be really hackneyed.
I have more confidence in the Giant's writing abilities than that though.