It sounds like you're more frustrated with Mom than the girls. I would have an honest conversation with her. Sat "I wanted to address our conversation from the other day regarding flushing the toilet. I want to just make things clear that this is my business that I run out of my home, that I can run how I see fit. When you used the word "forbid", it did not sit well with me at all and I want to be sure that in the future you show more respect for how I choose to run my business and if you have an issue with anything, then feel free to discuss your feelings with me without making orders." Or something along those lines. I do't think you'll feel better until you get it off your chest!