Pitching, like hitting, is an individual thing; typically the more (time) a player puts into practice the better she will become.
But practicing for the sake of practice is not the idea. Going out, and giving one’s best effort (with the goal of improving and stretching oneself) is the purpose of practice.
I often hear parents say, ‘My daughter should want to practice so I wait for her to ask me to help her.’ However, thinking your child doesn’t ask because she doesn’t want to improve might not be true.
Sure it’s possible, but it could be that your daughter doesn’t see the correlation between practice and improvement.
Your child may practice because it is fun, or fulfilling for her. It may boost her self-confidence to get the undivided attention from you along with your praise and recognition.
On the other hand, you may practice with your daughter because you know it will help her to improve. Bonding and helping her grow is in there too, but is that why you tell her you two practice?
If you want your child to practice more, make it fun and instructional.
Encourage her; focus on what she does right, or well, and praise her for it. If she does little well at least praise her effort.
Your daughter’s skill development should be something you work on together; eventually she will understand the value of practice.
Tip: keep the practice sessions short so when she asks to stay longer it’s her idea. It’s also okay to invite a friend to pitch or catch with her while you provide instruction.