Veneers would explain it, but it doesn't make sense completely. Why would she get veneers in the first place, and why would she refuse to dub her dialog over if she'd had the work done out of vanity? It seems like she had perfectly nice teeth before, but now she sounds a bit silly and appears to have an overbite. It would make more sense if she'd had some sort of injury that needed to be fixed.
It kinda seemed like her accent was different, too.
I'm not sure why I care about this, actually, except that it's puzzling.