Horror movie question: woman with mouth/lips burned off?

[Lemmy Lugosi]

Many years ago (very late 70's/early to mid-80's), I saw a film at the drive-in that I cannot, for the life of me, recall more than this about it:

A woman gets her mouth/lips burned off (or something like that).

I remember vividly what the effect/the actress looked like in the scene, but I can't remember a thing about the rest. Except that, for years afterward, my friends and I referred to the actress in that scene as "Katherine Hellburn". This subject came up in conversation today at a party, where some folks (old friends) were discussing fireworks accidents. We all remember "Katherine"....but no one remembers a thing about the rest.

Does anyone have any idea what the film was? Anyone? ....Bueller? ...Bueller?