From the Super Mario Wiki
Ms. Pac-Man is the wife of the famous Namco video game character, Pac-Man. She made her debut appearance in Ms. Pac-Man, a game originally created without the consent of the creators of Pac-Man, but eventually the rights to the character were handed over, and she has since appeared in other Pac-Man series games, becoming a staple to the series.
She has made crossover appearances in two Mario titles to date, Mario Kart Arcade GP and its sequel, Mario Kart Arcade GP 2, along with her husband and their arch-enemy, Blinky. Her racing stats differ slightly from Pac-Man; she has better handling than him, but lower top speed (in Mario Kart Arcade GP 2 she is a speed character). Ms. Pac-Man uses the same special items that Pac-Man does: Pooka, Rally X, and Galaga Boss, which are references to other classic Namco titles. She makes a cameo in her sprite form in the Pac-Land stage from Super Smash Bros. for Wii U.