Interesting that she can't. I'd expect a rep loss and her to go back to her usual schedule. Not that I would know what's going on with her, I haven't had Mirel move in. I'm waiting for the Custom NPC update to see if I can get someone else in there.
Glad, I could at least clear it up for you, I had a similar problem once, but I caught it early and reloaded to redo the first half of my building. Other NPC will look at buildings similarly, so if you want to expand another NPCs house or the Bathhouse, just build out from their building.
Out of curiosity, do you have a hoard room for your dragon character? Like an opulently furnished room with high valued items littered around. If you don't, it might be a fun to make one and give you something to do for your character, see how other NPC react to it.