Legal Question in Real Estate Law in Maryland

She cannot. If she continues to refuse you will have to file an eviction action in the Landlord/Tenant branch of your local Maryland District Court. If you lose any rental income because of the delay, you could seek damages from the holdover tenant in your suit. If there is an attorney's fee provision in your lease for breach of lease, you'd be entitled to recover those as well. I suggest you write her and point all these things out, including the fact that you relied upon her notice to re-rent the place. If you've already signed a lease with the new tenant, you might be liable to them for failing to make the property available.