Make a list - better yet a spreadsheet (parents love that stuff) off the most likely places the snake would hide in the room where the tank is - they rarely go far, they just snuggle into the first tight place they can find thats relatively warm. Drawers, under furniture, behind the books on a shelf, etc. Show her that you've already got a systematic search plan in order. Second step, dust for prints, so to speak. Keep a bit of flour handy, if you cant find him at first, sprinkle the ground and look for tracks the next day. Also, although i've heard mixed reviews of this technique, a "trap" consisting of a small hide box with a (safe) heat source and if possible a food item inside. Obviously you'll have to leave it overnight b/c its unlikely to come out if you're watching. The key is to have all this stuff prepared in advance to demonstrate that if the escape should occur, the resolution process can commence immediately.
NOTE: I reccomend searching this site for keywords such as "escape" or "find" or "lost" There have been dozens of post dealing with lost snakes and many of them have happy endings, you can learn a lot of tricks and get ideas of where to look by reading other people's accounts of lost and found.