Typically uncertainty & unpreparedness is the reasons for a lack of confidence. First get her mind focused on execution and off of results. (Focus on the process). Win and losing don't matter and will take care of itself. 2nd how much has she been practicing and have you had her practice in game like situations? Chance favors those who prepare. If you are stuck in a situation where she has to pitch then be extremely positive and take a no pressure approach. Focus on detail such as have her throw only her top 2 pitches and hitting the locations she is comfortable. As the game goes on and she is hitting her spots with those pitches then move into those areas. Have a go to phrase for her for when her mind gets off of execution and starts thinking about results. Example: You the number 5 to her which is a signal to her to say to herself something like, "Keep pounding" or "just own the next pitch". Something that keeps her in the moment and off the scoreboard and thinking about what has happened or is going to happen. Keeping them focused on the next pitch and ONLY the next pitch is the key and toughest job you will have." You can use this with hitting or pitching. With hitting keep it really loose. Remind her that she is not going up there to hit but to dance. Keep it fun and loose in both practice and game. When she is at the plate have her sing to herself and stop thinking. The thinking stops when she leaves the on deck circle and moves toward the plate. Remember she is a freshman and very young.
As a coach you help her to herself. Good luck with it. Improvement is the key not winning.