I have a work trip pop up this weekend, instead of flying back from BWI to SDF with my gf, I might have to fly direct to LAX. Since my gf is my companion pass ticket, what will happen if I don't show up for the flight?

Since there is a possibility that my work trip will cancel, Is there anyway to convert her ticket into pay ticket? Or should I just buy another ticket for her? Can I book her in the same flight as companion ticket, and cancel it last minute if we don't need it?