Once the flier got the grapple and we worked out whether they could carry their victim, I'd say each exchange flying up adds the flier's Athletics score to the potential damage. That'd be in lieu of any fixed stress-per-zone-fallen numbers.
If you ARE going with a fixed stress per zone fallen, then I rule that flying up while wrestling is a supplemental move, moving you up 1 zone and imposing the normal -1 penalty to your primary action. By contrast, however, if your victim is not fighting back, you can roll Athletics and cover WAY more altitude per exchange.
1 zone above the combat area doesn't need to be that high. It just needs to be higher than people can reach. 5 stress every 10 feet is the rule, so I was going to rule that you can only go up about 10 feet while carrying something heavy (that's actively trying to escape).
So, a 10 foot fall *shouldn't* kill anyone outright. The people on the hand-glider were considerably higher.
Also, I probably wouldn't allow anyone without a STR power to do this. SHe's going to have a Might Score of 4 and Inhuman STR, which gives her a lifting capability of 7 (a motorcycle...around 400lbs?). Now, just because she can lift it, it doesn't mean she can fly with it, which is why I was going with the 1 zone movement as a supplemental which is part of the grapple rules. I don't think she'd be able to to take-off 3 zones with an athletics roll...maybe if the person wasn't fighting, as you say.
The issue I have is this:
Exchange 1:She gets an aspect and tags it for a grapple
Exchange 2: she moves as a supplemental and then has the choice to drop the victim (Might vs Might) or continue to grapple (block)
Exchange 3: she moves up another zone as a supplemental.
What can the victim do? If he holds on, she'll just keep moving up and if he breaks the grapple, he will suffer a 10 stress fall.
She'll probably be able to control most grapples anyways. Do you think it's fair to do it this way? She's essentially taking herself and one other target out of the fight. She's not doing any damage until she drops them...it also takes her several exchanges just to do damage.