Should someone buy stuff for an anniversary party and bill you without first asking you?

My brother's girlfriend spend $148 on flowers, paper plates, corsages, chocolate, and Champagne for my parent's 50th anniversary without consulting me. She then gave me what amounted to a bill. I am a father of four and we are a home schooling family, so we are on a very tight budget. To give her the benefit of the doubt, she might have thought she was doing me a favor. When I told her that me, my wife, and the kids wanted to pick out some of that stuff, and that I thought Champagne and chocolate were unnecessary since no one enjoys drinking and my mom, for whom the party is being thrown, is allergic to chocolate, she became very angry. Am I obligated to pay this bill? Am I crazy to feel manipulated?