"Where does he get those wonderful..." emoticons...?
They need to face good pitching at 8u and 10u otherwise it's a walkfest at these age levels and the kids are not prepared as they move up in division. I think it's important for these kids to get proper instruction early on so the bad habits don't creep in and are harder to fix later on. Just like your example, had the father come to you first his DD would not have had so many issues with her mechanics.
When learning movement and off-speed pitches, there should already be a foundation of 'why' in place - which is the main reason I wait to work with pitchers until they approach the 'cognitive' milestones that accompany being 10+. The 'when' is, like Rick alluded to, a pregame or in-game process.... and it takes some work (not just from the pitcher). That said, fearing or not-understanding your opponents strengths - are horrible reasons for someone else to call their pitches... but sadly, some of the most common...
Very true in my experience with DD. We have always worked with the why. Just telling her to throw this pitch or that pitch doesn't really do a lot for her other than repetitive motion practice.
In 10U it didn't really register with her and I would get lots of shoulder shrugs with her answers. In 12U it started to click, but I could tell she would guess quite a bit at the answer when I asked her what she would throw for a certain situation/battter. In our first fall of 14U (still 12U eligible as an '00) she doesn't wait for the question, she answers before I can even ask the question with about 95% accuracy.
They will mature and if you give them the necessary tools to do the job, they will surprise you. Tell them the why so they aren't just a robot processing someone else's input. I would like to see more coaches work on the pitcher/catcher battery calling in 14U.