For some clarity, indoor zones in this game are designated like this:
Rosalyn's Shop
But if the indoor zone has subzones:
Rosalyn's Shop - Rosalyn's Bedroom
Rosalyn's Shop being the base zone here.
When Mirel first moves in, she will pick a random base zone on the shed plot to move into, that usually being the shed's base zone itself. You can create your own base zones and subzones by following the same formatting. E.g. "XXX's House - Bedroom" or "XXX's House - Storage Room". Really, there should be a custom UI that exposes this when starting a new zone, but currently there isn't.
What probably happened is that you deconstructed all the tiles of the base zone she was previously assigned to, and there isn't really a great fallback behavior for that right now. You can ask Mirel to move to any base zone you've created, which is what you should do to fix her.