Good question and it actually translates well into today's version of collegiate volleyball.
With the NCAA adopting 15 subs, the game has changed into front row - back row specialists; these specials may only play a couple of rotations. Gone are the days where 4 players go all around and 1 Libero replaces the MB's.
Now, teams are fronting/backing their setters/OP or their OH's/DS's. A DS will always serve for the other middle, with the Libero serving for first middle. This means that club players have to become comfortable and successful bouncing in and out of the rotations, and in/out in a moment's notice; not only for their club career, but for their potential collegiate career.
A suggestions for you and your VolleyPSA:
1. Don't stress about high school - With club dominating the recruiting market, high school volleyball is now just free touches in the fall to pass the time before club starts.
2. Because this is the new normal of collegiate volleyball, it is actually a good opportunity for her to learn this skill now, so she can succeed as she progresses in college.
3. I find that being active in the verbal support of the team, during matches helps 'stay in the moment'. She should be specifically complimenting players and plays. Instead of yelling, "great job", she should be yelling "great hit Amanda!". She may not be on the floor, but her voice can be there.
4. She should be as physically close to the court as possible; don't be at the end of the line of players at the end of the court. Coach's have impulse substitutions; she should be the first face the coach sees.
5. Do not engage in chit chat with bench players during the games. Coach's make impulse judgements when they look down the bench - Seeing players totally off in another world, talking about anything but volleyball will keep a player on the bench in the mind of the coach.
6. In side changes, she needs to grab a ball and do a light pepper with a team mate - Huge to keep a touch on the ball. If nothing else, is shows the coach you are ready to go in right now and want to go in.
7. When she knows she is going in (she is in a rotation pattern), she should verbally (in her head) go over what she wants to accomplish ("make a tough serve, communicate on serve, dig everything in my zone) - She needs to mentally pre-set her success.
8. These same tips can be applied in practice - Don't let the time in practice when she is not active, negatively influence when she is active; specifically cheer for players, stay away from chatting, be physically close to the drill, mentally pre-set when she knows she is about to go into the drill.
Your are experiencing the new volleyball, and honestly, the volleyball I am sooooo glad I never had to play.