Thats sucks man she was nice, same thing happened to me with my royal. Got it with a suncken belly, mine lasted a couple weeks though.
We had a a guy come in that specialized in plecos to our fish club and said that any sp. of pleco that eats wood has a specieal chemical in its stomach to better help digest it. He said that if they are poorly fed and dont have any wood to chew on by the time they get to us that the chemical can disipear from their stomachs, and that at that point there is no chance in saveing them or it is very hard.
I don't really know how it all works, but he said they have the chemical in them when they start out and when they lose it there is a chance that they can get it back from a healthy pleco in the tank that eats wood.
I don't know how much of this is true but he has videos of lots of rare plecos that he has bred and brought in a bunch of rare stuff to sell in my club.