It's a pain when a snake escapes! You can try leaving the mouse out - on a heat mat in a dark quiet corner, preferably under a hide.
Otherwise, start a methodical search of the room,moving out from the cage, making sure you check under behind
under, behind and inside EVERYTHING, even if you don't think she'll fit
(sorry computer is having a funny 5 mins)
They can wedge into tiny spaces if they want to. Obviously keep the door shut so you know she can't get out from that room. You can also try leaving flour round the edges of the room to see if you get a trail, or use crinkly paper. You are more likely to see / hear movement late at night so if you can spend a little time in the room at midnight with the lights off (have a torch to hand) you are more likely to see her.Also - don't forget to look UP! They can climb quite well so check curtain rails etc.With royals you often find they haven't gone that far, so pay extra attention to the area near the tank, plus double check all the warm places.
Othen than that it is just a question of keep looking. It may take a couple of weeks for her to surface.