I'm not happy saying this, but our centerfielder is an absolute disaster. We couldn't hide her if we tried, they would find her. She does fairly well on balls left or right of her. (good but not great) Line drives totally befuddle her, especially those right at her.
Not but one way to cure her problems. Literally, a thousand balls hit to her, left to right, right to left, straight back. Run her little legs off. Start now in practice, and in the off season make her really get after it. I did that with my son in little league right through high school and it turned him from bad (little league) to outstanding in high school. The best one in Orlando/Winter Park/Lake Brantley area. It works, if she has the speed and is willing to work at her craft. It also takes a dedicated coach and parent willing to put in the extra work.
She obviously has talent, it just needs to be brought out into the open.