About when did you notice your mama sitting on her eggs (fully committed, sitting almost all day)? And did she have all of her eggs when she first sat, or did she continue to lay for awhile?
I ask because I had a mama start sitting halfway through laying her clutch, so she sat at 10 eggs, but laid an extra 10 afterwards for 20 total. 1 died, 11 she hatched on her own, and I had to incubate the remaining 8 as they were far behind.
Have you candled the eggs recently, or do you have an incubator you could finish the hatch in? Usually mamas will abandon nest a day or two after ducklings start hatching, but I’m not sure if your mama would leave with just the one baby or not. If there’s still eggs alive and you don’t have an incubator, I’d be tempted to take Nugget away so mama can continue to focus on incubating.