OK, I'll weigh in with comments about large-breasted women since I am one. Bras and bathing tops are intended to be confining, so removing or unhooking it would be a good idea for CPR. To preserve modesty, a man's shirt or some other garment or sheet of thin material could be thrown over the chest without impeding compressions.
The woman who finally turned this victim to her side did the smartest thing, and not just because it let the fluid escape from nose and mouth.
From the large-breasted perspective, there are only three ways to keep large breasts from choking oneself - don't laugh, it's a serious concern. One can raise the upper body slightly up from a fully prone position, in which case gravity will keep the breasts downward of the windpipe area. Another method is to turn on the side, making sure the breast tissue isn't trapped up near the throat. Third, especially if the body MUST remain prone, remove bra and let gravity pull a breast to each side to clearly reveal the breastbone, zyphoid process and ribs.
I'm glad this issue was raised. Trainers don't even like to talk about it so I appreciate the opportunity to tell it like it is. If you watch the video again and notice how the victim's various positions affect where her breasts are, you can really see how they can interfere with breathing. I hope if I ever need CPR that someone will care enough to move mine out of the way of resuscitation efforts, which will also make a real difference in my ability to breathe.