Bea, is the main protagonist of this cartoon.  She is generally a very upbeat character - bubbly, energetic and personable.  Personable, is the key word.  She's a very sincere person so it's important to make her voice and delivery seem as natural and warm as possible.
She also has some tragedy and complexity to her character so she would have to be able to deliver some heavier lines while keeping an overall positive demeanor.

Even though Bea is supposed to be a cute child, it is not necessary that she needs to sound cute and childlike.  The most important aspect of her character is her conviction and openness.  It's important that she believes everything that comes out of her mouth.  She wears her heart on her sleeve so don't be afraid to really emote with her.  Yell everything if you need to.  It's better to overact than underact.