As long as she is listed on your resort reservation, she can use DME. You really don't need to 'do' anything special. Just giver her the voucher that comes in her name (in the packet you get from DME), then she just heads to the DME welcome area, the voucher gets scanned, and she is directed to the appropriate bus.
Even if she can't get the voucher before departure, she can still go to the welcome area and they will print her a new one to be scanned. She just has to be listed on the DME reservation listing.