We've had ours go missing for days on end, they always come back....eventually.
They sometimes think the grass is greener... then come home. If she's a "house cat" she's probably just enjoying a taste of freedom maybe. I know that probably isn't any comfort right now, but that's cats for you. If some one has taken her in, they prob won't realise she is a "house cat" and will let her out eventually, and she will be back. Hope it's sooner rather than later.
