That's because she's a civil servant, a permanent fixture, essentially a human-shaped desk tidy, and will never be fired. Having served time with many a doomed minister, she's also more than aware that nothing will ever change and everyone is an idiot. Such is her soaring apathy that she's not even that intimidated by Tucker. Got to admire that, if nothing else (and there really isn't anything else).
Played by Joanna Scanlan
At uni, Joanna Scanlan was mates with Tilda Swinton. Many of us would have rested on the laurels of this anecdote for... oh, the rest of our lives, but Joanna Scanlan went ahead and became a star herself after the usual years spent doing the usual small telly roles (she played the illustrious part of "Cellmate" in two episodes of EastEnders). The Thick Of It proved a real springboard, though, as Joanna went on to co-write and star in Getting On, the comedy-drama which could (lazily) be described as The Thick Of It in a hospital. Some episodes were even directed by Peter Capaldi and everything.