Easy answer...... Cut!
I have heard grumbling a from players about her effort. I can't fathom how she isn't aware she isn't meeting standards. We've had multiple talks about it. It also doesn't set a good precedent if I let one get away with not trying and still gets game action.
Sometimes the best thing you can do for a kid is to cut them. If she is really not motivated, she may be playing for the wrong reasons. If she wakes up and decides she really loves softball and wants to keep playing, you've done her a favor by lighting a fire under her. She quits and never plays again, you've done her and her family a favor by ending something that was never going to end well anyway.
I'd say at the very least she needs written up and an action plan put into place.