I know what you have experienced and this is "sniffing" the air to try to detect you due to some stimulus that she picked up on, but this is completely different than when a deer walks in completely down wind and picks up on a "visible" difference in the surroundings. If you have chosen a tree that is too small or not enough leaves to conceal the "blob" effect, deer, especially does, will pick up on this and look up at you. They may not react to it, unless you move, but she definately recognizes the change in her environment.