I have an old iPhone4 that I want to clear...trying to find the email and password attached to it.the phone has been sent to a person in Washington state...how do I unlock and clear it from here?

I have given an old iphone4 to a friend in need. It is in her possession. I am trying to unlock...when I go to find my it under my devices it is not included to unlock it. In the meantime she cannot clear it without my clearing it...she went into an apple store and was told I have to clear it, I talked to verizon...they said she may have to mail it back to me...as I cannot seem to connect it with the right email.and password. What can I do?