snowed by drifting in the purest google sense:

"I used to be pure as the driven snow, but then I drifted!". - Mae West(?)

Mae West's quote was actually "I used to be snow white... but I drifted." Actress Tallulah Bankhead, however, is supposed to have said "I'm as pure as the driven slush."

perhaps it is a Shakespearean Conflation:
Shakespearian, although it doesn't appear in that form in any of his writing. Shakespeare used snow as a symbol for purity and whiteness in several plays. In The Winter's Tale - Autolycus: Lawn as white as driven snow. In Macbeth - Malcolm: black Macbeth will seem as pure as snow. - The Phrase Finder