Ashley's a witch who lives in a haunted mansion with her familiar, Red. I don't think she even knows why she works for Wario, but her microgames have a distinctly morbid sense of humour that speaks rare volumes about her inner workings. She's always learning new spells and is completely detached from everything around her. You know that one kid in class who always got way into dissecting animals and thought everything else was like, so lame? That's her. A regular Wednesday.
It's not something I've really been conscious of directly while playing the game, but listening to them all side by side, Ann's delivery is probably the "peppiest" of the three. Erica does a decent job, but I still side with Jean because I think a very matter-of-fact delivery and the less-airy quality of her voice works really well for someone as distant as Ashley. Considering she was possibly a child when recording the game, I think that's a great touch that really defines Ashley for me, hearing a child talk and sing in such a dry, deadpan manner.