Want to start a new Castleville account on my iPad
This is likely because her Apple ID is being used for Game Center.  To fix will require that you have your own Apple ID.


Go to Settings
Tap Game Center
If you see her Apple ID, change it to yours


If that doesn't work, This is because the game either stores game data in iCloud or somewhere other than just in Game Center.  To fix will require that you check with the developer on which Apple ID affects game status. 

If signing out of Game Center doesn't fix things, then delete the app and all of its data. Then re-download the app. Lastly, before launching, use your Game Center account/Apple ID.