Collins (The End of Time)

Miss Collins was an employee of Joshua Naismith in the 21st century. When she was a child, an accident left some burns down her left side. After the Immortality Gate was tested on her, these burns were healed. Like the rest of humanity, save two, she was turned into a member of the Master Race by and was restored to normal by Rassilon. When Gallifrey appeared in the sky above Earth, Miss Collins fled the Naismith mansion in terror. (TV: The End of Time)

Behind the scenes
The script describes Ms Collins as 21 years old.