Essie, Vera, Zazzie, Pearl.
Star would also be a good nickname since the name means "Evening Star".
If you HAVE to have Vespera as your kid's name, then go with Vesi, V or Ves. You DO realize that she will be teased like, forever, in school and be known as Princess Vespa from the movie Spaceballs? For that reason I would change the name to Debbie.
Ves, Pera, V, Vesper, Vera, etc.
Scooter. Because, you know... Vespa.
Sting. Because, you know... Vespa.