If you feel like it's more pressure than pain, maybe try telling her tonight you appreciate her coming out so the team can play, and that she should just whatever she can and don't worry about the rest. Tell her if she hits the ball and can't run it out, that's ok, you appreciate her trying. Mostly, tell her just to have fun out there. It's just a game.
Perfect response. Reminds me of a guy I know. Head of a pretty successful organization in our area. Demands a high level of commitment, and effort in practices, and shows up at teams practices when needed, and is good at the "bad cop" role when girls need a little extra encouragement. I have heard him many times though telling girls to "have fun" during games. Don't be afraid to mess up...mistakes happen, but have fun.