Well, I think when people say she "fell down the steps", they mean she fell ON the steps, And when they say a photo shows her laying on the ground, they really mean "outside", as opposed to inside the house on the floor.
I still don't think she just sat down. Perhaps she spilled the stuff out of her purse and was bending over to pick it up, lost her balance/got dizzy from a bent-over position, and then just "let go" and fell the rest of the way. There's one photo showing her prone, on her side, with her legs sort of draped down the steps. It may be that at that point she extended her legs prepatory to trying to get up.
Supposedly there is a picture of her while "falling", so maybe we will get more info.
Video would be great, too....
Wonder what Nifong will spring on the defense today?