Hi Aimee! I may be way off with this, but I do have a book titled "Mrs. Duck's Lovely Day". It's a Rand McNally Junior Elf Book (smaller than Little Golden Books). My notation inside says I bought it in 198l; I bought it new, not used. The duck is white, and the cover is different from the cover you describe--my cover shows the duck wearing a red apron, standing near her old-fashioned black cookstove, and holding a cup of tea. However, the picture you describe does appear a few pages into the story. If you remembered the cover correctly, could be the cover picture was changed in later editions. Hope this helps!
I'm trying to find a book that I believe was called either, "Ms. Duck's Busy Day" or Little Duck's Big Day". All I can remember from the book was the cover and a few pages inside. On the cover it had a white duck near a pond, she was holding a towel over her wing and possibly wearing a bathrobe. It started off with her getting ready for the day and heading off to the pond for a bath. The illustrations were very busy and covered with detail. Sorry I don't remember more, but if I saw it, I'd know for sure if it was it or not.
Aimee