My old iPad is on Activation Lock

Here are the Apple support pages that outline the Activation Lock - and the only mechanisms by which it can be turned off:

Activation Lock for iPhone, iPad, and iPod touch - Apple Support

Turn off Activation Lock – Apple Support

As you will discover, unless you are the owner of the AppleID that was last used to activate the device, or unless you can secure the cooperation of the previous owner, you’ll not be able to defeat or bypass the Activation Lock. Without documentary evidence that you are the original owner (such as sales receipt showing the serial number), Apple won’t assist - and nobody here will be able to help you.

If the owner of the AppleID that previously activated the iPad has forgotten their AppleID or password, they can recover their credentials here:

https://iforgot.apple.com

To recover the credentials, they will need access to one of the following:

• The primary email address mailbox that corresponds with the AppleID
• Any of the secondary/recovery email addresses that should be configured for the AppleID account
• Any of the trusted telephone numbers (fixed line or Cellular/Mobile) that are associated with the AppleID

Unless you AppleID account has not been fully/correctly configured, or has been seriously neglected, recovery of the AppleID and password should not be difficult.

More information about recovery of your AppleID:

If you forgot your Apple ID - Apple Support

More information about recovery of your AppleID password:

If you forgot your Apple ID password - Apple Support

When you recover access to your credentials, you would be well advised to log-in to your AppleID account from a web browser - and verify/update any email addresses and trusted telephone numbers:

https://appleid.apple.com

This may also be relevant:

The All Too Common SAD Reality of Buying … - Apple Community

Tell her to use Apple's iForgot service or contact their Account Security team.

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