My next door neighbour had her paths professionally jet washed. Shortly after she heard scurrying noises in her loft. The pest control man found a small space at the base of her wall, where the cement had been blasted away. A camera in the loft revealed that she had a new tenant, which must have gone through the hole and climbed up through the air space in the wall. Poison dealt promptly with the problem, but she slept downstairs for weeks afterwards, and still worries, even though the access hole has been filled.
I don't mind the little beggars if they stay outside, and I rarely see one, but I don't want them in the house. I hope you manage to get rid of your visitor, Miss A, but old houses are difficult to keep clear. You definitely need the pest controller to come, before they start breeding.