Since she's never been out of the yard before, it's quite possible that she's very close, but hiding. Heck, my little house is only a thousand square feet and there've been times when I couldn't find someone who didn't want to be found. Cats are experts at "hiding in plain sight." You could try taking some clothing that you've worn and not washed and putting that outside; if she happens to be a little farther away, the scent might guide her home. Do follow Lisa's advice: GO the shelters in person and check everywhere. I remember Kuhio's tragedy (how Lisa and I met), and it still haunts me.

What's your cat's name? I'll add her to my nightly prayers, along with BeeBop and Sylvester.