Rent free in exchange for housekeeping

Single quiet room overlooking garden with own en suite shower, basin and toilet and small kitchenette equipped with microwave, frig and sink offered to mature non smoking woman without payment, in exchange for up to 12 hours help in the house of an active widow. The worker provides for and prepares their own food except if invited to share a meal. Compatible with study or other full time employment. Previous helpers have worked as a full time legal secretary, as a full time non-resident nanny or in catering or attended full time university courses in London.

What I am seeking is someone who will look after my house as if it was their own, and keep it in good order at all times, which means sometimes noting and doing what needs to be done rather than in a rigid programme. Previous helpers, who have become friends, carried out the major tasks (hoovering, dusting and cleaning bathrooms) in about 3-4 hours weekly at the weekend after they find their way around the house. Time for weekly ironing, cleaning silver and brassware about once a month, and help with catering, adds to the time.

It would be helpful to have references of any previous employment. I am not willing to have anyone, either worker or my own friends, in the house, if they smoke.
My helper’s friends are not to be entertained in my house.