If your DD is a pitcher, you will no doubt hear this softball jewel of advice on many, many occasions. Don't believe it...its a lie...perpetrated by softball fogies who don't know a thing about what they are talking. They will tell you that pitchers who have arm, elbow and shoulder maladies simply have bad mechanics.....or they don't work hard enough. BS.
Overuse is overuse. I didn't believe that when my DD was 9....I believed the advise I got...I fought with people who tried to warn me...and my DD paid the price. I don't like to talk about my DD on the boards, but I will talk about her in this single context. During her time pitching, I have had to take her to the hospital for a line drive to her pelvis, a broken finger from a line drive that required two screws in her finger and two surgeries, an appendectomy, and arthroscopic surgery on her shoulder to repair her overuse injury. They wouldn't do the shoulder surgery until I had taken her for two MRI's where she had dye needles injected into the joint in her shoulder for a better picture on the MRI.
The number of games and innings take their toll. Nothing is hurt by keeping these kids from playing 100 games per year until they are 12 years old at a minimum. Don't do what I did. Don't be like me...regreting that you didn't listen to people who could have saved your daughter from pain she will likely feel every day for the rest of her life.
Take a chill pill...relax...and slow her down...so that she will enjoy the really important times of the remainder of both of your lives.