I'll definitely throw in underhand throwing, thanks! I'll throw my wrenches at her to see if she can catch them. If she can catch a wrench, she can catch a softball.The best thing that helped my DD was just playing catch while throwing underhand. This is not pitching it is just throwing the ball back and forth underhand while playing catch. This is where she found the fine motor controls needed to control ball location. This is in a super casual setting.
I would be spending as much time with overhand mechanics as underhand at this age. Austin Wasserman and Dan Blewett are great sources(keyword Waterbottle drill). I would also use baseballs or tennis balls don't let the weight or size of the ball mess with good mechanics.
I would add a focus on fun-throwing days. We would walk through the park throwing rocks at trees or skipping rocks on ponds. To this day I still randomly play "Here Catch this" where I throw something randomly at her to see if she can catch it. Pitchers need quick reflexes when on the mound to defend themselves. The idea is to work skills without it being work.
I definitely agree this all should be fun. She enjoys pitching, even practicing. The only time she complains really is when the weather sucks or she's tired, at which point we stop practice.My daughter will tell her jokes with her catcher during wrist snaps. And that made her pitch better - because it loosened her up mentally.
She has been reading up on pitching and the other day said- I’m not supposed to wrist snaps with IR, am I? But I feel like they are important to my catcher and I starting up.
I ate lots of peanut M&Ms swimming D1. I’m sure that’s not best practice- but I swam better when I ate M&Ms.
Remember to leave room for fun/ weird traditions. It’s supposed to be fun.