What do you mean by "how about I give this castle to you?"
Does she even own it now? Didn't the state exile her family?
They did so I imagine she doesn't. But, the girl Does have some knowledge of the original plot even if she hasn't used it in a while because of her refusal to mind the rails. It's possible that sitting in that unused pool of knowledge there's something that someone who isn't exiled could use to obtain ownership.
Might have to do with why Evie ends up being a maid like we saw in that flashfoward. We still don't know what that was about