I mailed a book to another member. However it came back to me because her address was wrong in the system. She PM'd me to let me know that was probably why the book went lost. It's a WL book and yes, I did receive it back postage due. It wasn't forwarded because it was sent media mail. She asked if I'd send it to her again at her correct address and offered to give me credits or send postage to make up for the lost postage the first time.

I sent it to her the 2nd time using custom DC with the correct address. She buddied me 3 credits however I'm not sure if she's buddied me too many. I don't want to take any extra credits from her but I can't quite figure out if 2 or 3 is the correct number.

Help me please!

Scenario one: Three sounds correct to me.  If the book went lost, the credit would have been returned to her, so she owes you for the original mailing(1), then you paid to get the book back (2), And then you sent it back to her (3). 

Scenario two: However, if she re-ordered through the system, then PBS would have given you a credit for the last mailing (1), meaning she only owes you two, (1) for the original mailing and (2) for you paying to have the book returned.

Although, if she re-ordered the book from you (thus paying 1 credit through the system) it is possible she just buddied you an extra credit for the inconvenience.

If she gave you three credits then she wanted to give you three credits. 1 credit for sending the book , one credit for the inconvenience of paying again to send it gain. and maybe she gave you another credit for the package arriving to you postage due. You can always ask her to make sure thats what she wanted to do.

What everyone else said.  3 credits sound fair in this situation.

I sometimes just gift extra credits to people who have gone out of their way to be helpful, or who are brand new (and who I suspect have hardly any credits.) I know many people sell credits, but a gift is nice and unexpected. Kind of a pass it on kindness act. 

Yes, three sounds correct (as already mentioned).  But if she's going to mark the book received at the receiving end (as a current transaction or as a 'lost' transaction) she should only buddy two credits and the third will be transferred by the system when she marks it received (or when it's scanned at the PO if you used PBS DC only).