awww....she really IS hidden well. I bet you feel frantic don't you. Has there been any opportunity to slip out the door? I have had a "lost" kitty two times. One time was for several days and it turned out that Bert had been in the wall crawlspace in the attic. The most recent was Lizzie who went missing for most of one day. We never knew for sure where she went but later found the lining of our boxspring torn and think that must have been where she went. Boomer also disappeared into the springs under a couch. Maybe check extra well under boxsprings and stuffed furniture. Bet she comes strolling out to you by sometime tomorrow.

edit: I read that she is found YAY!! What a fright!!