You can't cancel her tickets or DDP. Those have to be the same for everyone registered on a package. But you can get tickets for everyone to match hers, and just upgrade the rest of the party to longer tickets. Or you can just eat the cost of her last day on the tickets. And the rest of the party can use her extra DDP credits. I would just leave the package the way it is, and if she needs DME arrange an earlier pickup just for her. Depending on the airline, there will most likely be some kind of charge to change her flight.