Sounds like you’ve read some of the same stuff I have!
My personal contention is that she started out high-strung and flighty, then got a little unstable . . . but I don’t think she was clinically insane.
(But I’m playing her nutty as a fruitcake, ‘cause crazy is comedy gold.)
And you're right, from a theatrical point of view crazy is a big draw, long as it doesn't shade over into SCARY.
But . . . how scary could a lady in medieval robes and headdress BE . . . .?
. . . uh, never mind . . .