Libero mistakenly leaves the court
 

Libero is on the court in back-left position. When her team wins the rally, they rotate, the middle comes on the court and Libero leaves the court through the replacement zone. Then her coach reminds her that it's her turn to serve, so she she immediately runs to the service area -- without re-entering the court through the replacement zone.

I didn't do anything about it. But the more I thought about it, I think technically, it was an illegal libero replacement. She left the court, which completes the replacement for the the middle who is rotating to the front row.

And THEN, she re-enters the court to complete the second replacement. Usually, the two replacements are done at the same time without the libero leaving the court. But once she does leave the court, shouldn't she re-enter properly?

Just can't remember seeing it before, so I'm trying to think it through.

Was she out long enough to be a UD when we came back in?

No

I think by rule you are correct, but I'd also ignore it or just mention it quietly to the coach.

This is the guidance I'd use. Especially since had she "done it right," she would never have entered through the replacement zone anyway. :D

Unless the coach was a jerk and now is paytime…😏