I'm guessing that when she slapped her the fruit bowl smacked her on the head as she fell and grabbed the table cloth.. ??? Unless someone came in and bopped her one ?? Naff "who done it" IMO .. probably wrong though :o)
In that episode, after Sonia left, there was a knock on the door and Pauline shouted something like "I'm not going now", probably thinking it was the taxi driver? It never did show you who knocked on the door, so I'm guessing it was whoever really walloped her.