Each guest is entitled to only one DME bus ride in each direction. If you are using DME on your original arrival day to get from the airport to your resort, and then later take a DME bus to get from your resort to the airport to get home to meet up eith your daughter, then you've used up your DME rides. You wouldn't be permitted another ride from the airport to your resort, and then at the very end of the trip yet another ride from your resort to the airport.
Sorry to be the bearer of bad news, but that's the way they do it.
It's not just a matter of asking Disney to be nice, assuming it doesn't cost them anything to have another person on the bus. I don't know about the trip from resort to airport, but I know for sure that on the trip from airport to resort, Disney pays a set fee per passenger to the airport and a set fee per passenger to Mears, the subcontractor that provides the buses and drivers. It's the scanning of the vouchers that produces this billing. A Mears employee (not a Disney cast member) does the scanning, looking out for his/her company's bottom line.