Hello!
Egg eating is something that lot's of naughty birds like to do. It is possible that Quacker (love the name, by the way) accidentally broke an egg, thought she would see what it tasted like, and then has been stuck with the habit since.
An egg eating habit can be broken several ways. You can use a gold ball or some other egg mimic and put it in Quacker's nest. She will eventually realize that pecking the "egg" doesn't give her treats, just a sore bill, and should stop.
Another method is a little more hands on. Get one of the eggs and poke tiny holes in each end so you can blow all the inside fluid out. Then put mustard, hot sauce, or both inside and put the egg where you can be sure your duck will peck it. She will be very unpleasantly surprised, as ducks and chickens alike hate the taste of mustard. The spiciness makes it even worse!
Whatever method you try, know that it will take a little time for your duck to learn.
Good luck!
~ClickCluckMoo~