I agree, this is frustrating.

However, if they think they're still on a drop in policy then I can't blame them. Yes, she should have given notice, but it sounds like her husband was supposed to, so I'd chalk that up to miscommunication.

From here... I would send her a contract advising her if she wants the space then she has to commit by X date. Maybe one week from now. And payment goes along with that.

You can't look for someone else because you made the mistake of not contracting. We've all done it, but it's not the clients fault. It doesn't sound like shes done anything wrong.