It is different. With, say, polish chickens, it's just the feathers that grow in a certain way. With tufted geese, like my roman tufted, it's just a ball of extra skin. With ducks, it's literally a hole in their skull that is then covered over by skin and the crest. This make it super dangerous...
Unfortunately the neurological problems are quite common with crested ducks :( The crests are linked to a fatal gene and if a bird gets two copies of it, it dies in the shell. With her two crests, I wonder if perhaps she did get two copies and somehow made it to hatch? Looks like you're taking...