well then......... not a bad thing that it probably isn't a seizure. I know they freeze like she's saying and that is most common but I didn't know if it would be possible to present physically different from that or not. I've seen another glider seize on a video but it was much more "violent" for lack of a better description, than your girl and it wasn't the freezing up that she described.
But there are many types of seizures so the visible signs may still vary I really don't know.
So if it's "probably not" seizures, could be neurological or as I said earlier an injury of some sort to her spine.
Gliders move in all kinds of crazy ways, it may have happened when you weren't watching.
No one's placing blame, just trying to figure out the cause because that type of movement is not seen very often.
So please know, it's nothing you could have prevented, even if it was an accident, and who knows she may have had a preexisting condition before you even got her. There is so much we still don't know about glider medical issues it is a constant learning experience for the whole community.
Your doing all the right things, asking questions, showing how she moves, going to the vet...... that's all you can do and your doing a good job.
Until she can safely have an xray there probably isn't much that can be done for her unfortunately. But vet visit still the best option for her n see what they say.