No themas if the lady decided not to leave on the date given for possession by the court the landlord will apply to the court for a “warrant for possession”. The warrant for possession is an instruction to the court bailiff who will carry out the removal of the tenant and others. The tenant may apply for the warrant to be deferred, but it is unlikely this would be granted, I have never known the court to defer the possession in the circumstances that are described.
Martin the lady would not have gained any rights to remain, this is the advantage of a assured shorthold tenancy that the tenant and others only have security for the fixed term, which must be a minimum of 6 months. The assured shorthold tenancy were introduced under the 1988 Housing act to breath some life into the moribund letting market in which landlords feared that they would not be able to recover possession of their property, without this act there would be a great shortage of property to let. The landlord has an absolute entitlement to possession if the correct procedure is followed.