Well, the way I see it, the plot of the movie revolved around missing princesses from Brooklyn. Well, "Daisy" is a normal name for a girl, while "Toadstool" is not, so that's why I think they used Princess Daisy instead of Toadstool. Plus, it added some more depth to the Mario universe, as now Luigi has a girlfriend (and doubles partner). Daisy from the games is the princess of Sarasaland, a kingdom Mario saves at the request of Toadstool. This game is Super Mario Land. Daisy is also in Mario Tennis. So, that's all.
