Your friend can do two things to help you:
She can unlock it remotely as part of preparing it properly to give to you:
What to do before selling or giving away your iPhone, iPad, or iPod touch - "Use these steps to remove your personal information from a device, even if you don't have it anymore." Click here --> https://support.apple.com/HT201351
If she cannot remember her Apple ID or password:
Click on this link to read what to do "If you forgot your Apple ID" --> https://support.apple.com/HT201354 Note that typically this is an email address you use.
Click on this link to read what to do "If you forgot your Apple ID password" --> https://support.apple.com/HT201487
or go directly to this link --> http://iforgot.apple.com/
If she has kept her original documentation she can request Apple remove the lock:
Apple can completely reset a device if a person can provide sufficient evidence of valid ownership. Do this online at: Activation Lock support request - https://al-support.apple.com/#/additional-support Apple says, "Proof of ownership documentation is required," but does not state what currently 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).
Click on this link to learn 'How to remove Activation Lock' --> https://support.apple.com/HT201441
