Alas, too good to be true.
Yes. Famous fake.
CGI.
It looks like a well-done fake. A hard-hit batted ball would take about three seconds max to get to that spot on the wall and the girl would have to have world-record speed just to get to the wall, much less climb it. Ball girls are usually SITTING on a bench in very shallow left/right field, so would have to run forty to sixty yards just to get to the fence.