A full grown mouse is a tad bit excessive for a snake her size, but a hopper is way too small. It may be she hadn't fully digested the adult yet and you will get something soon. I wouldn't go digging through her substrate to find waste. Any unnecessary stress in this time period where she is settling in is best avoided. Generally I use paper towel the first 90 days so it's very easy to see what's going on, but I wouldn't switch to that and further disrupt her at this point unless you have a pretty good reason to suspect something is wrong. If you can't see of smell it, it's probably not bothering her if it's there.