It really depends. I played tennis with a former racquetball world #1. He could easily start out at 3.5 maybe 4.0 and had the athletic skill to move higher. His strokes where pretty text book and I believe he played some tennis growing up as a kid so his transition was easy. Their is another former world #1 named Cliff Swain. It was rumored he was a highly ranked sectional junior, about a 5.0 tennis player before he went pro in racquetball.
Go hit with her and let us know.