Flights through Disney, adding someone to a package

[Tiresius]

I am booked for a September trip on a package that includes not only dining and tickets, but also airfare/flights through Disney. Now, my mom is thinking about joining me for the trip. I know that I can add her to the package only with all of the same package elements as me (same ticket option, same dining plan, etc). But is that true for the flight portion? Since flights are paid for and booked through an airline and not just through the WDW resort, can they be separated? Or if she is added, will she automatically be on the same flight as me? Its not a problem if she has to be on the same flight, but before I call Disney to investigate the price, I want to know what is even possible.