Did you mean you want to completely erase the iPad Air?
Or did you mean you are getting errors while restoring the iPad Air? If you are getting errors, could you please tell me what the error is?
Unfortunately, it is not possible to erase the iPad if there is an iCloud lock. You need the password ***** the iCloud if you need to erase it and make it working again.
iCloud lock is a kind of protection that does not allow others to use the iPad.
Are you not able to get the password ***** your grand daughter?
However, an Apple Store can remove the lock. But you may need to provide them with an ownership proof. Do you have an Apple Store nearby?
Can you please try the steps mentioned in the following website. Let's see if that works.