I know exactly how she feels!
The home party business gets old very quickly. Why call it a girls night out when it's a business transaction?
Buying out of guilt or "peer pressure" as Sussingham notes, is the only polite way out. After a while, the lure of a glass of wine and homemade goodies palls and you start inventing excuses...
I had to go underground to escape Pampered Chefs, Mary Kay and Tupperware.
Sussingham's suggestion that we drop the pretense of getting together out of friendship, and instead pay a cover charge to cover the cost of goodies and bring in a little cash for the host, is perfect. A simple solution.