Jade Yates was on the Greek island of Kos when she persuaded her mum to let her get a small picture of a flower put on her back.
But within hours she broke out in blisters around the design.
Jade is having a course of anti-biotics to treat her rash, but doctors warn that she might be scarred for life.
If her scarring is really bad, she might need plastic surgery to cover it up.
Her mum, Lisa, is very angry. She said, "These henna tattoos should be a bit of fun, but Jade looks like she's been branded."