Hello 'Mafromrm'.
Right, well on my IPhone 4G I have pressed the 'delete account' button in the ICloud settings before and alls it does is remove the ICloud account from your device and any data that is saved with ICloud will be removed from the device, for example contacts. If your contacts are saved with ICloud and you delete the account from the device they will be removed. How ever you are talking about an IPad so that shouldn't be a problem. Alls the 'delete account' button does is remove the data from the device that's saved with the account. It won't do anything to the actual account. Because you can just log back in again. I did it with mine and then I just logged back in again and all my contacts were restored. If you want to delete your sisters account from the IPad alls you have to do is go into settings, go into 'ICloud', scroll down to the bottom and press 'Delete Account'. It doesn't do anything to the account but remove it from the device (which can always be logged back into). And then basically just set up yours from there! If you're unsure just back up the data onto a computer. But alls it actually does is log you out of that account. Hope this helped. Missie Wong x