Margot actually seems like a good mix of Dr. du Maurier, Abigail Hobbs, and Wednesday Addams, no?
Apparently the average mare weighs around 1,100 pounds and a foal weighs around 10% of that. The placenta is around 10% of the foal's weight. So you have 121 pounds there. That's the size of an adult female actress, right? Wouldn't take too much more stretching to shove a creepy social worker in there.