It is a best practice to have all communication in writing — particularly when changing terms in a contract or ending the working relationship.
In this particular case, the termination was verbal rather than in writing. The termination is still effective as of the date that verbal notice was provided. If there is a discrepancy with the termination date, the facts will need to be examined to determine when the termination actually took place. In other words, if the contractor argues that the contract was not terminated, did she continue to perform work after the verbal termination date?
I suggest that you send something in writing to the contractor confirming the termination date.