What happened?

OK, so my female mated with a male. Then she went gravid. She had bumps, the triangular shape, the pre-shed lay, and everything. She even was digging in the nest box I put in the tank for her. Now it has been 18 days since her pre-lay shed, and no signs at all that she is going to lay eggs. Also, she no longer has bumps. She just seems very thick all the way around. Her thickness is more pronounced above her cloaca than it usually is, but she does not seem to be even close to laying any eggs. In fact, I am not sure she is even gravid anymore. Can that happen?

She very well may not have been gravid at all. What you saw and asumed to eggs my just have been ovulation. Or she may still be gravid and just hasn't laid yet.

One of mine goes through the full lumpy/nesting thing each year and has never laid so much as a slug. Eventually, the lumps just go. That's the "trick ovulation".

But if yours is still showing as slightly thicker, perhaps you'll have more luck. Keep treating her as though she's gravid for a few weeks and see what happens.