Mama Muscovy are generally attentive and good mothers.
Sometimes an inexperience muscovy Mama will need help to care for her brood.
Sometimes they will take against a duckling and ostracized it.
So you need to be attentive for 2-3 days as the ducklings hatching. As you have already been advised, the ducklings need feed, and drinking water but no bathing water at this stage. I use non-medicated starter crumbles. If she does well brooding her ducklings and keeping them warm for 3 days, you can relax as she should be OK
I don't wait until they are fully feathered to let ducklings have supervised swimming. But I am guided by the ambient temperature and how much sunshine there is. By three weeks old the ducklings need to be at around 80F but could bathe in full sun for 5 minutes and then dry off in full sun. I can do that at this time of year in Florida but elsewhere that might not be possible. By 6 weeks, all ducklings need to test their bouyancy and swimming skills briefly, most days. But they need a safe way to get in and out of the water -- i find a doormat over the side of a kiddie wading pool provides a long enough slope from the water and from the outside. But bathing should be supervised and not free access until the ducklings are 10-12 weeks and in full juvenile plumage