Need to move child onto their own Apple ID
If you set up a new AppleID account you will not have access to items bought from the iTunes store. But iCloud accounts are separate from AppleID accounts; she can have a unique iCloud account with her own contacts, email, and other settings, but will need to use the shared AppleID to have access to the apps, music, books, movies, etc... bought from iTunes.

There are some ugly hackish ways to get around this, but they sound like a waste of time and very sketchy to me.