OP, it sounds to me like you are not very familiar what goes into planning a wedding. When I got married, the church required a 6 month notification but it was more like 9-12 months to reserve the date/time I wanted.
The reception was worse. I was calling around a year ahead of time and many places were already booked for the date I had chosen with my church. After I finally found one that was the right size, the right location (not too far from the church but close to hotels for out of town guests) and the right menu and prices, I had to make sure the band and the florist were available.
Change the date? No, once the wheels started spinning there was no way I could change the date - even for a week. I would have had better luck moving it to a year later and basically start from scratch than move it a week.
You need to realize that what you asked (and are resenting) not only crossed the boundary of a normal, healthy, adult relationship but was also probably impossible for her to accomplish as well.