The girl lived in the 21st century. She was wearing a school uniform and texting messages on her mobile phone.
When Sarah Jane Smith, Clyde Langer, Rani Chandra and Luke Smith were chasing a Raxacoricofallapatorian, they stopped at the end of a street. There were tree people standing there, the girl, a granny and a postman. One of them could be the alien. Clyde thought it was the girl because she was texting on her mobile phone and might have been communicating with the mother ship. It wasn't the school girl she was texting to fast for a Raxacoricofallapatorian. (WC: Find the Alien)