How to get rid of activation lock if Apple ID is unknown?

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, you’ll not be able to defeat or bypass the Activation Lock. With documentary evidence that you are the original owner (such as sales receipt showing the serial number), Apple may be prepared to assist - otherwise they and nobody here will be able to help you.

If you have the necessary documentation, Apple have recently introduced a new portal though which you may be able to request release of an Activation Lock:

How to remove Activation Lock - Apple Support & start an Activation Lock support request.

However, your friend should be able to recover their AppleID credentials and remove the activation lock - using the following process…

If you have forgotten your AppleID or associated password, these can be recovered here:

https://iforgot.apple.com/

To recover your credentials, you’ll need access to any one of the following:

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

If you were the original purchaser and can prove it with

a receipt from Apple or Apple authorized iPad retailer showing

the serial number of the iPad, make a genius bar

reservation and bring in the receipt, iPad, and government

issued photo ID to Apple and they may assist in resolving the problem.

If the iPad was purchased used or there is no receipt, the AppleID and passcode must be recovered 

It is highly recommended that you make a Genius Bar Reservation to avoid delay at the Apple store

https://www.apple.com/retail/geniusbar/

It is completely impossible to get past the activation lock without using the Apple ID and password of the to whom it is registered. Without access to those, you have a useless device that should be turned in for recycling.

You need to speak with your "friend" to get her to unlock it with her credentials; sign out of her ID .and then factory reset it.

If your "friend" can't/won't help well you might as well throw the iPad in the bin or better recycle because it's useless.

BTW those companies that buy back phones/tablets won't touch it either.

No one else can help not even Apple .