Cally Simpson, from Arbroath, is being treated in a hospital in Barcelona, Spain. She was on her first family holiday abroad when the accident happened.
It had been hoped that she was showing signs of improvement after brain activity was detected, but there are now fears she may be unable to survive once off life support.
He mother Kate Miller posted on social media yesterday saying: "She's had her scan today and it wasn't good news. Her brain is really damaged and it's a huge concern."