As you can imagine there are a number of possibilities about what is going on with an animal when it has not eaten for a week or more, none of them good.
IME, these are the typical reasons and some things to try.
Stress
Check your saline, ammonia an nitrite levels and do a large water change even if they are fine. The water change is more for what you can't detect than what you can, checking is to ensure something has not gone wrong that is not obvious.
Try stick feeding a piece of thawed shrimp the size of its eye (no larger) and touching the arm as close to the mouth as you can manage. This is often difficult but make several attemps.
Leave a small active fiddler (large claw disabled if male) in the tank. It should survive for a long time if it is healthy.
Remove any fish you have in the tank. In spite of my rants, many people leave their cycle fish in the tank. This may not be your situation but I feel it necessary to mention since you have not posted anything about your environment.
Brooding
Usually a female about to brood is ravenous and very active just before laying eggs but Beldar slowed her eating just before brooding.
Here is a link to her thread as she approached laying eggs. Reviewing the thread, she had stopped taking shrimp but would eat fiddlers.
The collection of shells for a den does make brooding a distinct possibility. We have no journals (that I can remember) of macropus hatchlings (Bel was likely too young to have mated when she was captured and she is the only female I have kept of this species). However,
almost all macropuses are small egg species so the opportunity to raise even one is nil.
Senescence
IME, the macropus identifiable senescence is short. They stop or slow down eating over a week or so and then turn a very detectable gray. Additionally, they tolerate daylight and may be seen in the open in the early morning.
Not good news, I know and the best hope is stress that may be correctable.