You are certainly correct that every child is capable of handling different amounts of extracurricular activities and responsibilities. It's not unusual for a seventh grader to juggle sports, music, and school. The question to ask is, "Does your daughter feel comfortable with her current amount of responsibility and activity?" Is she feeling stressed out? Is there ever any time for her just to "be"?
Here are a few more questions to ask and discuss to discover whether her life is too pressured:
Are all her activities ones she is genuinely excited about? What pleasure does she get out of them?
Is she participating in any of these activities because she thinks you want her to? Because of her peers?
Is she "building her portfolio" for college already, being the well-rounded student that guidance counselors, teachers, and parents tell kids colleges want?
Does she have a real passion for any/all these activities?
Does she worry about her ability to keep up with her schoolwork with her current extracurricular schedule?
I am not giving you definitive answers on how much is too much because I don't know your daughter or her inner emotional life. I am giving you some key questions to ask yourselves and to bring up in discussions with her. She may flourish and be very healthy at all levels with her present life schedule. You need to give her permission to always reevaluate her activities in light of how she feels inside on a daily basis about the comfort level of those commitments. And it goes without saying that she needs to know that you think she's great no matter how many activities she's doing.