Charity got my full attention in "The Player" and her stunning looks worked well with the character because she had plenty of commanding dialogue and even some action scenes.
While I was glad to see her again in this Christmas special, unfortunately, the show didn't give her much to do other than look impossibly gorgeous in that red dress. (Seriously, if she walked down the street dressed like that, EVERYONE would forget to breathe, cars would crash into each other, etc.!!!)
It's funny, as a regular viewer it just seems blatantly obvious how to capitalize on someone like Charity, but somehow they've missed the boat. I suppose in all fairness the writers may have just put in the character without much thought and Charity happened upon the job. But some other epic Doctor Who episodes come to mind with female characters where it all just worked: Sophia Myles in "The Girl in the Fireplace", Carey Mulligan in "Blink", Kylie Minogue in "Voyage of the Damned" and Katherine Jenkins in "A Christmas Carol". In all these cases you simply cannot ignore the fact that these women are impossibly beautiful, and yet their time on those episodes goes far beyond that

I do hope we see her again in Doctor who. I thought she was really good.