Um ... isn't The End of the World Nine's second episode where Rose nearly gets burned to a crisp when the sun shields are turned off? Cassandra's first appearance in the show - she made her return in 'New Earth' which was the one set in the hospital and was Ten's first proper episode.
This!! For some reason I adore this episode, I just thinks it's great
New Earth is good too. The final scene with Chip telling Cassandra she's so beautiful makes me sad