It seems that if Jaina hits the opponent with her jump A high enough, she won't be able to combo afterwards.
...and I thought I was just bad.
I didn't have much time to test it for at least a couple of hours though, so maybe give it a double check!
Right, by design, as is common in fighting games, if you hit too high then you can't combo. So it matters to try to be in position to get a solid hit. In other words, if you use the worst possible timing and spacing, it doesn't lead to as much damage as if you were positioned a bit better. And there's still a large leeway of spacing to do it correctly.
I'm used to air nornals always leading to a combo on hit, so I literally just thought I wasn't hit confirming fast enough. At least I know what to work on now.
Air normals always leading into a full ground combo is an NRS-specific thing, I think - Fantasy Strike uses the more common and more traditional method of requiring a "deep" jump attack to link hits afterward.