How do you manage a team with 18 kids?

This season the JV team I coach has 18 players on our roster. It has been an extremely difficult task managing the team and making sure that everyone gets enough playing time. There are a few girls on the team that are exceptionally good at both defense and offense and they have received the most playing time this season. The majority of the team has split time pretty evenly and there are a few more that have played the least. Since the season is coming closer to an end we tried to get everyone into today's game. One player in particular has had a lot of playing time this season at third base. However, third base is not her preferred position. In the off-season on her club team she is primarily a catcher. On the JV team this year we have three catchers. The reason the girl I'm speaking of has played third base most of the year is because she is by far our best third baseman. Today was only the third game she has caught all season long. Her first game she did pretty well and then her second game for some odd reason she did not play to the best of her ability. When I watched this kid play today as a catcher, I was amazed and disappointed all at the same time. I was amazed at how fundamentally sound her catching skills are. The other two catchers that have played the most over the season really struggle with framing the ball and throwing the ball down to first, second or third. The girl who got to catch today does a phenomenal job at framing and throwing. There were multiple pitches thrown today that were not strikes but because of this girls ability to frame and sell a pitch to the umpire it really helped keep the pitch count down for our pitchers. She also threw three girls out today trying to steal second base. The reason I'm disappointed is because I did not give her a chance more often at catching. I felt absolutely terrible that she did not get more opportunities. Something else I noticed as she was playing in the game today was that she was making better contact with the ball when hitting and it gave her a lot more pop to her hits. In the beginning of the season she was hitting really well but as the season continued and she didn't hit as well as we thought she would I couldn't figure out why. I think now it is because she is more confident in her game while she is catching. Something I have experienced lately with my slow-pitch teams is that when I play in the outfield on my woman's team I hit around .750 and on my co-ed team I play a different position every inning and my average is .250. Thinking about this made me feel even worse about the situation because had she been playing at catcher all season long she would have been more successful with her hitting this season. I feel that as a coach I made a poor decision having her play third base more than catcher. After the game today I pulled her aside and spoke with her parents letting them know how much I believe in their daughter as a catcher, that she is by far the best catcher we have on the team and that I hope she doesn't give up on it. I also apologized to the kid for not giving her more chances to catch this season. Fortunately she is only a freshman this year and has three more years ahead of her in this program. If I'm lucky enough to work with the program next year and if I'm lucky enough to have her on JV I want to give her the time she deserves in games as a catcher. This is one of the many problems of having 18 kids on a roster! I wish I had more control over the team. I would have made sure we only had 14 kids max. If I had fewer kids on the team it would make it a lot easier to make sure everyone gets more playing time.