Wait, didn't Ganthet enlist Batman AND Green Arrow as well when he was getting heroes together to take down CrazyPants!Hal?
They don't have powers either, and Dinah can kick ass with the best of them (and really, she'd be no more or less effective against a godlike being as the rest of them in a fight). Unless I'm forgetting something and Ganthet specifically wanted her for her sonic scream in the battle for some reason...?
For oh so many reasons: goddammit, Marz and Dooley.