Try this...
During the day, get a bunch of plastic grocery bags and lay them along the baseboards, behind and under furniture, and any other areas that look like possible snaky thoroughfares. Then, in the evening, set yourself up with a quiet activity such as reading a book or something. No music or TV or computer games...just quiet. Let your ears be alert, and listen for the tell-tale rustle of plastic bags.
Leave the bags in place as long as necessary...always staying alert for their sounds, even when you're not actively listening. She may surprise you sometime.
Good luck!!