In an earlier version, the toll that saving the group took on Fr’Nj was going to be more personal; it was going to age her a bit… not to make her as old-looking as Faereksch’Nj, but maybe closer in age to Syr’Nj. Or maybe just streak her hair with white. Just enough of a mark to answer the question of “Well, those are some pretty awesome Graiya-like powers she’s got, why isn’t the team using those ALL THE TIME against EVERYONE AND EVERYTHING?”

As it is, the reason for her reluctance is fairly clear in dialogue. We can presume her increased use of the power in the last few chapters will be in line with what’s going on here: she is (not coldly, and not without regret) guiding plant life to sacrifice itself, to stop a force that would otherwise kill much more life than the sacrifice. It’s just that in the last few chapters, her idea of what that force is will have changed. Alliances shift.