Shiro's panic at being high up lead to a rather immediate and perhaps... excessive response. If she got bigger, then she would be closer to the ground without actually falling as far. Therefore, she should get as big as possible, as fast as possible, and fall as little as possible. Maybe the other people that had appeared in the air would appreciate it? Her scales and flesh had to be better cushioned than the earth of the clearing.

Perhaps it was the size change overwhelming the safe landing, or perhaps it was simply sheer mass, but the result was quite unmistakeable... most of the clearing was temporarily full of winding coils of white snake whilst everyone else landed one way or the other.

And anyone watching from the trees couldn't possibly miss the ground shaking from the enormous impact.