The Revenge of The Unmentionables

What on earth was Sarillia thinking, when she involved herself with The Immortals? And how did it occur to her to start fighting against The Unmentionables a fight that had already been won by them? Couldn't she just have shut her eyes to the slaving life of The Mine Children? Couldn't she simply forget about the hidden children in the forest? And go on living in The Green Valley, like she did now?