Silver is now burying her water bottle in all the bedding, which is a problem, since we want her to be able to drink fresh water, and not have the bottle leak into the bedding.
But look at her tunnel! She actually has a tunnel at the bottom, going to the back of the cage. As best we can tell, the tunnel then runs the length of the cage, where she digs in the corners. She also has a topside exist, unless she just poked her head up through the bedding by accident.
The bedding is also getting a little high and, for a gerbil, a little overripe (which is saying something considering gerbils don't have noticeable odor). So tonight or tomorrow, Silver's cage will get excavated significantly, and she can start over.
I kind of hate to do that, because she's enjoying the burrowing so much. But it needs to be done, if nothing else, to keep the water bottle uncovered.