I’ve been thinking about this, and can certainly see it’s something a character might want to do and therefore we should be able to *try* to kill Ethel after getting her hair. I am less convinced that we should be able to succeed.
The choice we currently have, between power and ridding the Sword Coast of a dangerous being (or killing or letting survive a really cool character!) is a meaningful one, and I think it cheapens it if we can have it all. Plus, it would mean there was no reason, after a bit of meta-gaming, for pretty much any party who wanted to kill Ethel to do anything other than have a go at deceiving her first, which would make the end of the fight more same-y.
I’d be fine if Ethel were given an out. She’s had a bit of time to regroup while you’ve been bargaining with her, perhaps that’s given her the energy for one last invisibility spell/potion and sprint to one of her faerie rings to teleport away.
