I lost a mouse

I had two bigger mice and two baby ones that were recently given to me. they're in a glass 20 gallon tank til I can get them something better. but earlier today I was handling one of the babies, I put her back in the tank and i ended up taking a nap. when i woke up she was nowhere to be found. I've taken everything out and checked through all their bedding and still nothing. it's a glass tank so she couldn't have chewed any holes and there's nothing close enough to the top that she could've used to climb out. what do I do? I have three cats and they aren't allowed in the room they're in but I'm afraid of her getting under the door and them getting to her before I do...