Mine laid 22 before she stopped. She slowly (over the course of the 5 weeks if incubation) threw out 5 eggs. They were all rotten, but the remaining 17 hatched. If you have a drake with her, even if you haven't seen mating activities, they should be fertile and therefore should hatch. Just remember that muscovies take 35 days to hatch, not 28 like other ducks.
i have a duck at the moment who has 18 eggs amd isnt sitting, doesnt seem odd except for the fact that she had a different lot of 15 that i took away because they got frozen over a few days of bad frosts(the outside taps froze up!), and i took the first six away to eat for brekky. so thats 39 all up! she's sitting on them and night bout no feathering up as yet.