There's nothing wrong with pitching and weight training on the same day. However, the pitching and skill-specific work should come before the weight training.
Pitching and sport-specific work is mostly power-based and can be technical if working on mechanics. You don't want fatigue and soreness from weight training to affect her mechanics while she is pitching.
It also depends on the athlete. Some like to get all their work in on the same day and use the next day as recovery. Others like to only pitch one day, and then get their lifting session in the next day. In this case, the pitching still came prior to the lifting session.