Well, I suppose you could take the, "You always need to be ready because you never know when someone might get sick or injured, etc." route. I think showing up even when you know she won't be playing is a great way to show your support, and even if she doesn't appreciate it now, she likely will someday. Really, on a JV team, I think it is kind of lousy of the coach to not spread playing time around a little more. Not that you should intervene w/the coach, but maybe this is one of those "life isn't fair" lessons, and being a team member means doing whatever you have to for the cause, even if it means honing your pine-riding cheerleading skills.
I remember those days well. Similar to PP, no JV when I was in HS. Only played my sophomore year. I think I still have the newspaper clipping from the Fri. double-header of prom night, when none of the jrs & srs showed up and the coach was forced to play me. I went 4 for 4 in one game! Sad to say, though, that experience really sticks in my mind as the one and only year (from the time I was 8 until I was pregnant w/my dd @ 38!) that I did not look forward to playing summer softball. I didn't go back the next year - was too busy with a leading role in the spring musical - or so I justified.
Does your daughter have good friends on the team? I was only friends with one other girl on that softball team. However, while I, too, was more mediocre at volleyball, for some reason it was just a lot more fun for me. Maybe because the team was loaded with my group of pals. That one I stuck with for 4 yrs.
You are doing a great job encouraging her, but I agree w/PP, if she wants to do something else next year, encourage that as well. In any event, sticking with something is definitely worth encouraging. But encouraging a variety of extracurricular activities, and exploring what she really enjoys is even more important.
One of the best learning experiences I ever had was making the JV basketball team my freshman year - when I really could not play basketball! It stunk, it wasn't fun, I wasn't getting any better and...it was one of the few things I ever quit in my life! Guess what? The world didn't end, I didn't become a lazy loafer, and I learned something hugely important: Sometimes, especially if something isn't working for you, it is really ok to quit. That notion came in handy down the road in a particularly difficult career situation which ultimately led to a career change!
Great job helping to keep your dd's chin up!