I've tried first turn Fellella plays, but I haven't explored that option as thoroughly as I'd like.
What I've mostly used Fellella for is followup on a Mana Flower -> animal play. If my opponent is occupied with my animals, and my mage is a few zones away from the action, Fellella lets me gear up rapidly, pressure my opponent with curses, and protect my creatures. They may focus on killing Fellella, but I can typically get several actions out of her first in this situation, since my opponent's creatures are a few zones away with my creatures hindering them.