So, I recieved a book today from someone. This book has never been ordered by me (I checked the transaction archive).

After further investigation, I realized I had ordered a different book from her, she never responded, and the request went on to the next person in line. So I'll be getting that book from a different member.

Anyway, what do I do? Not only did she not agree to send me the book I wanted, even if she had, she sent me the wrong book...do I offer to send it back if she gives me a credit?

I'm confused.

She must have responded at some point to get your address adn then didn't mark it mailed.  I would PM her and offer to either send it back or to the person who was supposed to get if she gives you a credit to cover postage.  She may have sent the book you originally ordered to the person who ordered the book you got.  Very possibly she didn't mark that one mailed either.  Tell her that the book you ordered has already been ordered from someone else and so you do not need a copy from her. 

If she doesn't respond after a while then I guess you can just post the book.

Sarah - yes, PM her and let her know that she sent you the wrong book. For her to have your address she had to have printed out the label for your request .- Did she accept the request and didn't mark it mailed?   If she wants it returned or forwarded to another member she should buddy you a credit to cover postage.  If she accepted but didn't mark the book mailed it would have automatically canceled and moved to the next sender in the FIFO line. If this is the case I would let her know you are receiving the book from another member, so you no longer want the book you original requested.

I pm'ed her on 9/19- according to my sent messages, she hasn't read it. I put the book in my TBR Mt. but in an easy-to-find place so I can mail it off if/when she responds. Odd.