Just seen this interview with her
She speaks much better English than Ray Winstone and he has become one of the UK's biggest actors. I recently saw an interview with Winstone and I couldn't believe an actor had such poor spoken grammar. It seems to be OK to speak badly if you're from London (EastEnders is another example) but not if you're from further north.
Neither of them need to have great grammar but clear diction IS required. Winstone reads other people's words, he's not a writer. Same as Cheryl doing an advert - but the fact that one of her lines in her current advert is, IMHO, open to an unfortunate but hilarious misinterpretation purely because of her pronunciation proves she should polish her skills.
Nothing to do with being "posh", just being understood.