The way you charge a ball in the OF would be unlike anything you would really do at third base, SS maybe (although you don't see many softball SS charge using 1 hand like you do in MLB). Anyway it is possible she is just taking her eye off the ball to peak at the runner? When you hit them to her does she have the same issues?
This...my DD used to bobble OF grounders, and 95+% of the time, it was because she was peeking at the infield. Lots of different types of grounders plus a buy-in on her part about the problem cured it.