Never mind....I found the answer....I should have read a little bit further down on these posts.  Thanks Mary....Yea, I just saw that other post....you guys are most helpful.

Sorry :)

Hmm. It sounds to me like she didn't mark it mailed and let it time out.  You don't owe her a credit. Look in the help docs, copy/paste the info and PM her-in fact there's another question where someone asked the same thing earlier today.  It's not your fault that she didn't mark it mailed and you shouldn't have to pay for 2 copies of the book. You do not have to send the book back to her.

Wendy, the Help Center guidelines state that if you receive two copies of books from a situation like yours, you are only obligated to give the current transaction (the one you CAN mark received) credit for the book.  The other sender is out of luck credit-wise because they did not follow site guidelines and mailed a book for an ended (canceled) transaction.

You would only be obligated to give the first sender a credit if you had not received another copy of the book.

There are many reasons why someone would send a book after it was canceled, but it should never be done here so as to not create this very scenario.