"Didn't think you'd be one to care about debts," she answers, going back to settle on the bed. She isn't really expecting anything in return, except maybe a future unwillingnes to sell her out or something to that effect. What are friends for?

And he hasn't been a problem to her. Honestly, it's nice to have someone to talk to who isn't so easily phased by the details of her life. And neither of them has the highest opinion of the Doctor. There's a familiarity there, and she hardly cares about pleasing the authorities, or about making his life difficult. She's just not a very spiteful person, not unless she has reason to be.