A personal representative takes the place of the deceased owner regarding maintaining estate assets. Therefore, if someone has moved uninvited onto estate property, they can be removed through the process of eviction or, if no money has been paid, through a process known as "ejectment" (which is like an eviction for a non-tenant but a faster process). In fact, depending on the jurisdiction, if the sister has not been on the prmeinses for more than about 30 days then you can contact the police and report her as a tresspasser. In any event, take no self-help measures such a changing the locks, turning off the utilities, removing belongings, etc. You could fing yourself in legal trouble if you do. At this point, you may want ocoonsult directly with a local lawyer who handles landlord/tenant cases as they can best advise you further.