We have one iTunes account for the family (4 of us).
Husband has a HUGE music library (on actual CD, plus CDs he had and uploaded, but no longer has the physical CD). They are welcome to download pretty much ANY of the music in our library (husband has clean taste and there isn't much that is inappropriate for a child even your daughter's age, but ours are 13 and 16).
The kids use the same account to download apps, and while we have everything set up on a credit card, they use iTunes gift cards to make their purchases. We keep a log at home of who has was balance, since we keep a positive balance on the account and nothing is ever charged to the credit card. The kids do not have the password, so they have to have one of us put in the password to make any purchase (songs OR apps), and in-app purchases are turned off for all of our devices, so that isn't an issue, either.
All in all, it works well. If one of the kids wants a song or app, and buys it, the other can have it also, no extra charge. Same with all of husband's 155 MB of music, which he is adding to continuously. They actually like a lot of the same music, so it's really nice.
Alternately, we could have set up separate iTunes accounts, and each person had only their own devices attached to their own account, and all hard copy music could be uploaded as desired to each account (a lot of work), but then apps would have to be purchased multiple times, too.
I know with the new family cloud sharing (or whatever) iTunes has, we could set it up differently now, but we haven't bothered. It works fine for us like this so far.