If only my friends had let me do this. They said it was too hard.
Yes, this.
I guess you can play games and wait for her to respond, but there are faster ways to get the info, and if you actually want a friendship with the woman after her wedding, you'll take one of the faster ways. Most brides are under tremendous amounts of stress and pressure while planning their weddings, and you are probably not going to get a dress ordered now anyway, because you're beyond the timeline. The timeline was probably put there by the dress store.
During my own planning, I found a line of separates that had nice tops, and the store would let us order JUST the tops...my maid of honor loves to sew, and her dad worked for a store that sold real, good, bridal fabric, so I got a lovely silk dupioni and my friend made everyone long a-line skirts to their measurements. One friend waited ages to order, and was really stressed that it was not going to arrive in time. Another friend ignored my firm statements that she HAD TO get herself measured, and to order the size that the measurements told her to order, to not go rogue and order what she WANTED, and ended up with a top WAY too small for her. Ended up having to rush order a new top, and ended up paying something like three times the cost of the top, because of it. Totally her fault, and while I felt bad for her, I knew that everyone had told her (and she was the first-married of my buddies, so she of all people should have known!).
These timelines are given to brides by the stores, and need to be followed.
But it doesn't sound like you want a relationship with her anyway, so maybe you could just have the kindness to TELL her that you're out? I had a friend pretty much disappear after I'd finally chosen the separates line; she never responded to emails again, and except for a "is that you?" facebook contact (which I deleted immediately) years later, I never heard from her again. It was sad at the time, but... (what was annoying is that it was her body-type that was throwing off everything for getting ONE dress, so I went through the trouble of finding something that could really work for nothing! It was also the cheapest way to go, at about $70 for the top and something pretty low to pay for my maid of honor's time...and the price point was also lowered for her budget)