Even if what the author says is true about medieval upper caste people (I don't doubt it), I have trouble believing that peasants could afford the cost and time required of regular bathing. Water didn't come easily unless you happened to live next to a river or have a well next to your house. We've all seen women in third world countries carrying water for cooking and drinking on their heads, often long distances. And we haven't even gotten to the costs of the other things she mentions. Poor people rarely ate meat because they couldn't afford it; where are they going to get animal fat to make soap?
The author doesn't provide any evidence, just makes claims using words to imply you're stupid if you doubt her. All the "photographic" evidence she provides all pretty clearly DO NOT depict poor people.