If you really are her friend and other friends will be there too, then just go and have a fun time socializing with your friends. Have a bite to eat (there is always food at the home parties) and a drink and when the order forms get passed out, just slip it back into the catalog and put it on the end table, say good bye to your friends and let them know you have to get home now, or stay and mingle a little if that's the situation.
That's it. If you are really a friend, then be a friend. Be there just to support her, I'll bet that's all she wants. She'll know you didn't order from her in the end, but that's ok. At least you came. If she gives you a hard time about not ordering anything, remind her that you already told her you weren't interested in the product, but came to support her anyway and when she has parties with products that you like you always order for her.
Do you really want to do something spiteful? I don't think so. I know it's irritating, but sometimes people do things without thinking about how others might take it and more often than not it wasn't intended that way. No need for drama or a drawn out invitation contest. Be the bigger person and assume the best intentions out of your friend.
To have a good friend is to be a good friend.