I always told my parents I DON'T FORCE kids to do what they don't want to do and if toilet training is so important to them, to take a week off work and do it at home, otherwise, nope.
Also, remind her that you forcing her child to sit on a potty can be inferred as child abuse and the law expressly prohibits you from using any form of physical force with a child and that INCLUDES making them sit on a potty when they don't want to. Centers don't do it for that EXACT reason.
If she insists you train her daughter, tell her that you will offer her daughter an opportunity to sit on the potty and if she says no, it's no so don't forget to send pull ups.
They are doing it only because they don't want to spend money on diapers after the age of two, not what's best for their child. Kinda eats into their wine budget.
