I don't think the writing is ofensive. But druids can be any neutral alignment. From neutral good, true neutral, legal neutral, chaotic neutral and neutral evil. Kagha is neutral evil.
Kagha is not human, but it is humanoid. And Tieflins don't upset the natural order more than a human. As far as chapter 1 goes, zentarim and the inn or the goblins are a bigger threath to balance.
Tieflings are quite literally creatures with extraplanar heritage. They carry the nature of the lower planes within their blood. At best druids would see them as diseased abominations, at worst they would be seen a corruption of nature. Humans and tieflings can't be equivocated in this case, because humans are a natural/native part of the world of Abeir-Toril and part of it's natural order, while tieflings are quite literally outsiders by nature. I would fully expect druids to dispatch extraplanar creatures on sight or to banish them.
Kagha not being human has no bearing on the issue at all. The point I wanted to make is that only humans are human, so talking about "human rights" makes no sense, especially amongst people who stand for untamed nature as opposed to civilization.
Also, the goblins being a threat doesn't mean that tieflings are suddenly not a threat. I think that if Kagha decided to exterminate them both, she would be authentic to her own professed value system.
Sylvanus himself is a morally unaligned deity, he doesn't care if his followers kill children or do things that would be considered evil. Sylvanus just wants results.