Hi, +Richard Bremer
and thanks for the comment!
It depends on the gym, but I'm usually working at ISO 10,000, give or take. That lets me shoot at 1/1000 or faster at f2.8 or so. When you view the pictures, you can click the blue "i" thing in the right column and it will expand and give you some brief exif data for the shot, too. Somehow, I lost the exif on #28's shot, but the others have the data.
This is one time the gear makes a difference. ISO 1600 won't get you there as you've found out. I use a Canon 1D IV and 70-200mm f2.8 (What a great lens!) to get these. Sounds like you've got the right glass. And I'm pretty sure these shots were selected from a burst ("spray and pray"). That's where the 1D IV's 10 frames a second really help!
If it's the camera body limiting you right now, maybe you can use the volleyball angle to convince her you need an upgrade! Good luck! :-)