This is a very broad question Witz, and it's a little tuff to respond to, except with a scatter-shot answer.
A. ?Are the girls seeing an actual pitching coach on their own, already? ?Usually a pitching coach will give "homework" for the girl to be practicing between sessions, and so she will probably be working on this several times a week on her own.
2-3 times/week in addition to the session with the coach should be plenty, (nobody needs to pitch every single day, imo.) ?In fact, it may be harmful, you have to let the muscles rest, and almost all coaches will advise the girls to ice the arm/shoulder after a session (a bag of frozen veggies works just fine, and you can use Saran wrap to hold it in place
) , and possibly take an anti-inflammatory afterwards, as well (Ibuprofen or Motrin).
B. ?Much depends on age and skill level. ?Beginners are working on basic mechanics and getting the ball in the general strike zone. ?More advanced are working on "hitting their spots" and on the details of specific pitches (change-ups/drop/rise/screw).
I know it sounds counter-intuitive, but when my dd started pitching, her coach stressed speed over accuracy. ?Get the mechanics of a great fastball down first and then just pitch literally thousands of balls without worrying over location. ?It's amazing, but in time, ?the accuracy will come on it's own.
For the older girls, hitting their spots is one of the most important parts of their arsenal. ?One drill is to have a girl pitch 25 balls to each of the strike zone "spots" (high inside, high outside, low inside, low outside). Tip---have the catcher keep track of which ones are actually hitting their intended targets, and then do an extra 25 of the particular pitch that is NOT as accurate. ?(Have girls actually write down these numbers, and save them to show you, and to compare themselves to when they next practice).
C. ?Will the girls each have a catcher at their disposal? ?Many girls do not have a parent/friend capable/willing to catch for them. ?Girls, don't let the unavailability of a catcher stop you from practicing.
?DD would sometimes go down to the local school and pitch against the side of a
windowless brick wall. ;D ?She would take her boom-box, a bag of balls, and mark her spots with chalk on the wall and just have at it. ?(Bonus, sometimes they would come back at her pretty fast---so she got in a little fielding practice, too!
)
D. ?There are general conditioning exercises pitching coaches will recommend (most are easily done at home and require no special equipment).
Can't overemphasize the importance of good quality push-ups.
?A favorite of dd's coach is to put a softball on the ground at center of chest spot, then try to lower yourself down far enough to touch softball each time. ?Tends to prevent the girls from just dropping to the ground---OUCH!
General stretching is very important for a good fluid arm swing. ?Big, fast arm circles (forward and backward) are good basics, also having the girls clasp their hands behind their backs and lean forward and attempt to bring their arms up over their backs as far as they can. ?A loose, smooth arm swing generates more speed than just trying to "muscle" the ball over the plate.
WELL---I've gassed on wayyy too long, (longest post I've EVER made) ?but I hope you can pick out a few things to help, or at least point you toward a more specific question.