I just had a very similar experience with mine. Monday she stopped taking food (frozen shrimp). She would grab it, fiddle with it for a minute, then throw it out of her burrow.
Tuesday, she took a piece and held on to it all night, but didn't eat it.
Wednesday morning she was out of her burrow in the middle of the tank motionless, but twitching a bit. I tested and my nitrates were over 20. The past Saturday when I did my weekly maintenance, they were 10.
I did a 20% water change and left for work hoping to come home to some good news, but when I checked at lunch, she had passed. There was some uneaten food in her burrow from when she was just holding it Tuesday night.
I got her from YourFishStore.com and had her just under 3 weeks.
I don't know if the high nitrates were the result of her not eating or if they were the cause. I thought she was getting ready to molt, so I didn't think anything was wrong when she stopped eating, but now I wish I had tested that day.