Sometimes an actor is given a special introduction as a form of compensation. The most common are "And," "With," and "Featuring." "Introducing" is often used to call more attention to lesser know actors when the studio doesn't want to pay more money. In this case the budget was cut so they gave her the credit since she was already getting paid twice, for acting and writing the movie.

Other times it's just a joke like Ocean's Eleven "introducing Julia Roberts".