If there is no formal written tenancy there is legislation in place to create a "statutory" one, a tenancy at will.
Does she have anything in writing she can rely on and proof of past payment of a certain amount of rent on a certain date such as a rent book and bank statements? Has the tenant paid any rent previously (how much is it?) and, if so, how and how regularly, was there ever a pattern of payment on a set date?
Are they a sole tenant or are others living there (agreed by her or not)? Do they rent a room or the whole place?
When did they move in? If not exact, was it more or less than 6 months ago?
Facts such as these can help estabish any supposed agreed terms of the tenancy.
She needs to make sure she serves the correct notice properly so that she cannot be accused of unlawful eviction and get into more problems. She could see a lawyer to get them to assist or see the Citizen's Advice Bureau should be able to help her with the finer details and filling in and serving the actual forms.