Green could potentially be a gender-swapped ringmaster, gender-swapped Timothy the Mouse, or an entirely new character created specifically for the film.
Green could easily be voicing one of these characters, but there are other possibilities.
She could also portray one of the clowns that appears in the film, in a (presumably) larger role than they played in the animation.
What this report doesn’t tell us is which role Green would be up for, or whether she is being eyed for a live-action part or to voice one of the CGI characters.