She really needs to work on hitting the pitches that give her the most trouble. Good 16U teams are usually well-coached. This means some coach is going to see the holes in her swing and make sure she receives a steady diet of pitches that exploit those holes. Good pitchers will simply execute those pitches with greater consistency than she has been used to seeing so far, and that is what is causing her BA to slip.
And by "most trouble" I don't necessarily mean the pitches she strikes out on. I tend to call pitches that I know girls will get themselves out on, even if that means a pop-up, weak ground ball or fly ball to the outfield. She needs to learn to not get herself out on those pitches!
I think you're spot on. ... Goal recently and moving forward is to see as much live pitching in practice as possible vs. quality pitching. Front toss will be more about hitting difficult spots. I think her front-tosser (me) is probably guilty of enjoying her smack one, so I'm too accommodating.