It's part of the normal growth process for ducks to periodically molt (lose and regrow their feathers). I've noticed color changes in mine after a molt. How old is she?
Yep, she is going through her first adult molt. It is normal for them to stop laying while molting. She will probably start laying again after she is done molting or she may stop for the winter and pick up again in the spring. It kind of depends on the breed and the individual duck.
While molting she needs more protein in her diet to help her grow new feathers. I feed mine Purina Flock Raiser, so right now they are getting that straight because it is 20% protein. During the rest of the year I mix in oats or grains to reduce protein. You can do a quick search here to find the different ways others increase protein.
It depends on the duck actually. I have one that dropped almost all her feathers in two days. She looked like an animal got her. She is now all done and laying again. The others are still dropping feathers.
Sounds like she is a slow molter then, lol... I have both types as well in my Calls... and varying ages... their pen and our yard always looks like ducks exploded in them, lol...