I know this will not help you find your sister. But the building is still there it was a house belonging to the Duke of Sutherland. It is still there at the moment. It became part of the Royal Hospital in Wolverhampton. People used to have to go there for colbalt treatment some years ago. I remember as a child playing in Gordon street as there were works happening in the building to get it ready for using the building for that kind of treatments. I have aunts and uncles that lived in the area and will enquire with them of its use.