From the experts:
Mellie is not Millie and it's not Nellie, though it will forever be confused with those too more familiar nicknames. It's cute, too, and while some of the names it's usually short for may be sailing into the sunset (so long, Melody!), others like Amelia are rising through the ranks and may give Mellie a new chance to shine as a cute girls' nickname. Just be prepared for endless confusion.