Okay, she is completely out of line in thinking she should be "paid back" for standing up for you. When you accept the invitation to be an attendant, you accept that it will be a financial investment and gift to your friend. But you are certainly not taking it on as employment!

The last wedding I was in cost me over $2500. The dresses were $350, the shoes were $275, I had to fly to AZ for a super swank bachellorette party at an expensive spa resort, to NC for the wedding and our accommodations were $350 per night. But this woman was my dearest friend. I'd have paid anything to be there. And our gift was a pair of simple earrings. I was so happy to be there for her.

Your friend is being selfish and should pickup a book on wedding ettiquette. Guess you won't have to worry about her giving you a nice gift