Bloom is a Main Character before auditioning do have a look at the links 
Princess Bloom is the princess of Domino as well as a Guardian Fairy. She is one of the founding members of the Winx  and is recognized as the group's leader. 

About her personality 

Bloom started off as an insecure girl in the beginning of the series because of her ignorance of her true origins and her strange, yet surprisingly potent powers. Later on, as she learned more about magic and herself, she grew increasingly curious about her past and whom her biological parents are. An escapist by nature, she has a tendency to run away when things get too hard or confusing for her, and can also be impatient and stubborn, with a short temper.

I would love to see your own interpretation / adaption / own creation of Bloom's  voice however if you need inspiration her a voice click the link's below

https://www.youtube.com/watch?v=nFtHjo5V734

https://www.youtube.com/watch?v=BUcNjksrogQ

VOICE: a very determined voice and some times can be quite fiery