Tahn Jeraveril was from Bula. She was captured by slavers but escaped. She enlisted a traveller to bring her to Earth.
On Earth, she gave her name as Avril Trelawney and posed as the ward of Father Martin. She arranged to meet Ben Jackson and Polly Wright, hoping they could get her in touch with the Doctor. When that failed, she decided to wait for him, knowing how often he visited Earth. (PROSE: Do You Dream in Colour)