Is her current layout pin up or pin down, and is the ball polished, and what grit is the surface at? My wife has the same exact problem with her Messenger Ti, about 10 mph and a good release with lots of backend, but struggles to keep it from going brooklyn or through the nose. Hers is pin down under and just right of the ring finger. She has the best luck when I keep her ball regularly polished with a couple of coats of Storm Reacta Shine, which is getting the ball towards 1500 grit, from its' original 500 grit cross-hatch polished with Degree 2000. Once the polish starts to dull in the track area is when she really struggles, so I'm just re-polishing by hand after every 3 games, and she is doing better.
Try a good polish and don't let it dull out, and see if that helps. If her current ball is pin down, maybe try a pin up layout with a longer pin buffer on whichever ball you end up choosing.