OK here is a link that kind of explains where glycerin comes from
What Is Glycerin?
taking that info, someone ***could*** make soap from peanut oil, you could also make soap from bacon fat, and beef dripping but in these times you don't really need to. Most commercial soap is inexpensive fats like palm & coconut.
I would say read the label and look for a peanut allergy warning. In the ingredients listing it would have the warning if it had come in contact with peanuts at all. This is the kind of thing the FDA should be watching out for.
hth
