Okay.  I got a slightly damaged book, which is readable, but I would not repost it for fear of having the next person get angry with ME for its condition.

I gave the sender the option to return my credit or not, but I wanted to let her know about the condition of the book so she would be aware next time.

She returned my credit, but wanted the book back.  I no longer have her address anywhere, right?  So I PM'd her for her address.  Is there any other way to do this or is this what I should have done?

You are not required to send the book back.  If the sender wants the book back, they should buddy you an additional credit to cover shipping.

Yep, that is the right way to do it, but you are not required to return the book.  As per the Help Center:

A requestor does NOT have to return the item in a "problem" transaction

• if the sender wants the item back, he or she should send postage or a credit to pay for its return.

so they would either need to send you 2 credits (one for returning the credit for sending you a bad book and one to pay for postage), or send you 1 credit and money for postage.

more than likely once the sender realizes they have to either send you an additional credit or send you postage they will more than likely not want the book back.

Thanks, ladies!  I'm goin' to get my extra credit!  Let's see what happens...