As well as planning permission she needs to pay business rates instead of council tax on that % of the house that is used as a B&B . This is quite complicated as she will have to claim expenses for the business as well and set it against tax. Probably easier to just rent out the 2 rooms on a monthly basis, if there is a university near then the accomadation office will be happy to help her rent the rooms to students , there is always a shortage of student accomadation.