She later escaped into the Battlefield universe and shagged the Doc like she always wanted to

Lady Christina de Souza (played by Michelle Ryan) is a thief, a liar, and potentially a murderer. She and the Doctor had a pitiful adventure that scarcely justifies recounting. It was a bit like Midnight only if there was no tension or drama or acting talent. Lady Christina steals things, which is wrong fun, and speaks the Devil's Armpit Farts. She's always ready for any emergency...

Many people say she should've been the next companion after Doonuh, and even Christina herself remarks that she and the Doctor would've been good together, buuuuut no. While a sassy thief as a companion would've brought an interesting dynamic to the TARDIS, Michelle somehow managed to make Christina terribly uncharismatic and dull to watch, to the point where sitting through just one episode of her was tedious enough. What's with the RTD one-offs having such shit actors? Even Donna was like that at first.