Juno was the title character in a film of the same name. It's not a film on the level of
Harry Potter (the
Hermione example again) but you might want to be aware that exists and perhaps differentiate your character a bit from that one (if you continue with
Juno). I can't suggest much on that I'm afraid because I saw it once when it first came out and didn't like it. Was 15 years ago or so now so I can't remember much at all.
Tomboyish nicknames with long feminine names;
Catherine /
Katie or
Kate
Francesca or
Francine /
Frankie or
Fran
Georgina or
Georgia /
George or Gerogie
Wilhelmina or
Willow /
Billie
Cassandra or
Cassidy / Cassy
Kimberly /
Kim or
Kimmy
Elizabeth /
Lizzie or
Eliza
Nichola or
Nichole /
Nicky or
Nikki
Harriet /
Harry
Jacqueline /
Jack or
Jackie
Danielle /
Dan or
Danny
Frederica /
Fred or
Freddie
Melody or Malanie or
Melissa /
Mel