administrator account with parental control? what is the use of having a parental control on and administrator account?

I have a mac where a 12 years old girl is using, she can do what ever she like (install apps, chat, etc) but want to have restriction on web sites against porn, etc

currently she has admin account, and I see that i can activate the parental control on! I did and it worked, but she can change the settings? my test shows she can not, what do you think?
Just create an admin account for yourself, where you know the password, and create a standard account for your daughter. 

If she wants to install something or do something 'admin-y' that you approve of, she can ask you and then you can go and type in your password to change it (Mac's can do this without needing to have the admin account logged in, it will bring up a dialogue box where you type the admin name and password so it's easy for you), however you can also set parental controls to block only somethings, so you can enable app installing etc., for your child, while still blocking sites.