If it is at the end of the lease it is a non-issue: if your lease is for a specific # of months then you have legal remedy if notice is not given. Call your local state's attorney's office for the law in your state and county, and you can also go on the web for free legal advice.com

 Go to the library and get the NOLO Guide to Landlords and Renters. It can give you the legal answers. She is not necessarily entitled to get her security deposit if she breached her lease and verbal notice is subjective and never a god method for communications. Also most leases state, any correspondence should be in writing.

You can't show the apartment until she gives you a written date of termination which is another point that is in your favor since it threatens your income from the apt.