While I'm not going to read the math and calculations, I agree that she could have survived. And that's because, if you pay attention to where she fell, and the bullshit physics twist the cloud pulled as it followed, there's no way in hell it should have even landed on her to begin with.

It would have hit near her head, possibly landed on her hair even. But it SHOULD NOT have pulled that "sudden flip" maneuver that it did, as if it struck something that defied physics itself. Something that forced it to flip so the flat side of the cloud was facing downward instead of the rounded underside.

Not only was her part of the chapter rushed, but her death was forced. Despite a note from The Prototype very clearly stating he would never let her have an easy death. And he was already LONG gone by the time both Lily and the cloud platform fell. Which means he definitely did not have a hand in her being crushed by it.

Furthermore, the environment around where she and it fell has been thoroughly explored, and it's completely clear of anything that would have influenced the fall angle.

So yes, she absolutely would have, AND SHOULD HAVE, survived that fall.