What you're encountering is:
"Activation Lock for iPhone, iPad, and iPod touch" is a security feature, one aspect of which is deterring re-selling of stolen devices. To learn more click here --> http://support.apple.com/HT201365
The person basically took ownership of the iPad by using her information to set it up.
An activation lock can only be removed using information for the account that applied the lock. If you know this information follow the onscreen steps to enter the Apple ID and password used to set up the device, or enter the device passcode.
How to remove Activation Lock - https://support.apple.com/HT201441
If you do not know the required information get the owner of the account to remove the lock.
Otherwise:
- Apple can completely erase a device if a person can provide sufficient evidence of valid ownership. Do this online here --> https://al-support.apple.com/#/additional-support Apple says, "Proof of ownership documentation is required," but does not state what constitutes proof. Prior to this new online service Apple typically required the original receipt issued by an Apple Authorized dealer and documented provenance (so typically it would be the original owner who does this, or a descendant with legal proof of ownership).
Typically an enterprise would use MDM to manage Activation Lock and Lost Mode --> https://support.apple.com/HT202804