If you are using OSX, you should be using separate accounts on the computer. As an administrator, you can select what programs that your daughter can run on her account (including the 'installer' app). This is something that you can do for free within the operating system.
A search for 'OSX parental control' and 'OSX web filtering' on Google may provide options for blocking certain web sites. There are a few reasonably priced applications out there.