Look at the way her head dangles, it's way above the ground. The web was tightened so there was no way it could have hit the ground. She died from the whiplash, her neck snapped, and her hair hit the ground. The sound was of the web tugging completely and her clothes touching the ground/neck snapping.
I seen the movie twice and I made sure to check it the second time. It's her hair that hits the ground, NOT her. That's the point of the scene. She was so close to certain death yet Spider-Man saved her if you view it in that way, but as we know she didn't survive the whiplash.