It depends on the girl, I guess. My daughter is a first year U10 and started pitching about 6 months ago. She throws an average of 5 days per week, but would throw everyday if I'd let her. Typically, she throws at practice twice per week (1hr each practice), with her pitching coach once (1hr), and a couple of games (usually 5-7 innings each) on weekends. A somewhat unique thing about her, though, is that she is around 5ft tall and 95lbs at 9yrs old. With that said, I think that it depends on the physical and mental make-up of your daughter. If she's having fun, wants to pitch, and you see no adverse physical issues, then I'd let her pitch on multiple days each week. Just keep a close eye on her...