She's living with the Clayr by the end of the book, and the story implies that Sabriel's/Lirael's dad will have two children, at different stages of his life, with women from the Clayr, so I guess that's what Sabriel's mum becomes as well.

I want to ask if it's more of a Dante or Bosch Hell lol

Definitely Bosch — there are a lot of weird chimera creatures in the Chatelaine's army, and Hell itself is a kind of weird giant creature thing that surfaces from beneath the Earth and disgorges its infernal horde.

The author also said it was inspired by a Bruegel painting.