The hardest things with these young ladies, is that they want immediate results. Most of us who come onto this forum know that hitting as well as pitching takes countless hours of practice before you see results. I guess what I am getting at is, your DD may fight you on moving from the machine to the tees and soft toss work, depending on her age. You may have to get her coaches to verify what your saying before she will believe that what you are telling her is truth.
Start your hitting sessions off of a tee, then move to some soft toss, then onto the machine. Make a point of telling her, when at any point her mechanics start to fail your hitting session is over, ....or you will drop her back down to the previous execise until she regains her technique. Give her some incentive to continue working hard at each station to reach the goal of hitting off of the machine. I would say that 75-100 swings per session max, fatigue will start to set in, hurting swing mechanichs, so know when to say "thats enough."
Another great tool on the market that I swear by are those Hit N Sticks, they cost about $50 and last quite awhile. Allows you to get numerous swings in different zones, without chasing balls. Also allows you to be right there watching her swing to provide immediate feedback and make corrections. Good Luck to you and your DD!!