li bingbing dubbed?

Was Li Bingbing's lines dubbed over in Cantonese? Because her lips didn't move in sync with the words spoken. Unlike the rest of the Cantonese cast members, she's from Beijing and speaks predominantly Mandarin so it wouldn't surprise me if her lines had to be dubbed. But why not just use an actress who speaks perfect Cantonese instead? I'm really curious as to why she got cast....