Since leaving the show, Katherine, 36, has gone on to star in several highly-acclaimed dramas including "Mr Selfridge", "Happy Valley" and "The Night Manager."
And later this month she will be headlining in ITV's "Him" and BBC Three's "Doctor Who" spin-off "Class."
But Katherine reckons she should be thanking one show in particular, reported Digital Spy.
"I always thought, 'OK, Becky's drunk again, but why is it this time? Is it because she's happy she's getting married? Is it because her marriage is failing and she's drinking herself into oblivion?'
"And I was a better actor for it - massively. I just think you get out what you put in, and if you put a lot in... it's like a ping pong match with the writers, and they will pick up on what you're doing and send you something great back.
"And when do you get that time on television to make mistakes? You just don't really.