I can't recall using Princess Daisy in the older games, but she's a decent character in the new Mario Tennis Aces game.
She's an all-around character like her assumed-boyfriend Luigi and his brother Mario.
And she plays decently well. One of my toughest tennis matches was against a Princess Daisy player and it was a challenging win for me.
Though she's not my favorite in the game, but I wouldn't mind playing as her every now and then.