How does a wireless TV splitter work?
If the signal source for the main TV is only an aerial, it’s a real challenge. First, you’d have to add a splitter in the aerial’s downlead, with the 2nd port going to a separate over-the-air tuner. The output of the tuner would need to be connected to a device like the Sony Wireless TV Transmitter/Receiver system (see the link). So that would be two expensive purchases (plus the splitter), and your friend wouldn’t be able to change channels in her room. She’d have to go to the main room or wherever her separate tuner is located to do that. There is no better way other than somehow bringing an actual signal source into her room.