Don't have Heidi do that.
So.
Heidi Klum is gorgeous. And part of her appeal (besides her flawless appearance) is her cute German accent. (If there is such a thing?)
So, Victoria's Secret, when you have her singing "Santa Baby" in unaccented English...
it's creepy. Either because she's lip synching to something that's not her voice, and it's obvious, or because we're like, "But Heidi Klum has an accent, so, why can't she talk like that normally?" And it bothers us.
So - my suggestion is this: Have her sing with her German accent. It'll be better, and less weird, and we won't remember that Victoria's Secret had that annoying commercial that made us think about things besides Victoria's secret -- like German accents. And cheating.
That is all.