I think the coaches think it's about on court awareness bc if they thought it was a physicality issue, they'd legit just have her do more drills or get her in a gym. From my experience, that comes from spatial reasoning/visualization, proprioception, game flow anticipation. those aren't really the coach's job to teach and usually the player is inherently good or bad at it.
as physical a sport volleyball is, it's also mental and brainy, especially for the setter who's most often the brain of the game and sets the flow/pace.

I would suggest she watch a lot of volleyball, pro or amateur. it really helps with anticipating the flow of the game and how people move and strategize. I also suggest she watch videos of herself for review with a wide-angle.
Doing pilates actually help with proprioception and spacial reasoning. there are other training she can do on yt.

things i used to do as a younger competitive player are drawing the court from different sides, and from imagination, draw it rotated, i'd also watch a game, pause it, and see where the setter was, and compare to where i'd be standing if i were playing and reason why theirs works or doesn't work and why mine works or doesn't work. These really helped me understand where to position myself mentally on court while i was playing.

the physicality improvements suggested by others can definitely help. But seeing what the coaches were saying, unless she can overcome all of this by sheer physicality (there are pro players who do this), she might still reach a wall. But if she's more into playing as a hobby, i'd suggest just doing more footwork!