Wether the hag is part of nature depends on the definition. For me in our world all is part of nature, the humans are not excluded. I don't like how the "super-human/elven/dwarven/..." world of the Forgotten Realms is constructed in DnD, it often does not make sense, but it is a given. If we take it, the hag is part of nature because she exists.
But that all is part of nature is not an argument that all has to be accepted. You can support a lot of world theories and ideologies just by changing the point of view. So it's a philosophic question. I tend to refer to an utilitaristic view here, I think the world for the most is better with Ethel removed. That would be a bit inconsequent in our world because Mayrina, whom I try to help all the time, violates the principles of a developed Utilitarism. But in the FR it seems to be possible to revive the dead, so Mayrina is not acting that strange.
