I finally got a chance to watch the parade on line last night. The commentators did mention that these girls are not soldiers but college students from some kind of specialized combat medic school.
I think there is a difference between militia and regular troops in China's parades. Just as the name implies, militia is composed of civilians. Much like reserves, they go back to their normal jobs and lives after they are done with the specific missions assigned to them. In the case back in 2009, their mission was the parade. So once done, they would go back to their every day jobs and lives. And I would imagine they might go through some military training a couple weeks annually...
With the regular troops in the parades, I believe that they are actual soldiers, but their primary job is to train for parades, much like honor guards. The PLA is huge. So It's not difficult to find a couple hundred soldiers in each branch of the service and train them for parades.
Sometimes, they have non-combat formations too in the parades. The commentators would specify that they have a formation composed of cadets from military schools. I guess the nurses/medics that we saw this time would be this case.