I agree. Personally, I think that she just wanted to ask a question to ask for opinions and advice, in response to a mother being angry with her.I also have to question whether opinions would have been different if the OP had stated that they were on the autistic spectrum rather than having a sister on the spectrum? I know it's difficult, but we have try to stop seeing NTs as almost like a different species.
Being a teacher who deals with small children, I can see both sides of the argument: Yes, children, especially older ones, sometimes lie and ask to go to the toilet as an excuse to get out of the lesson, to go and use their phones. Yes, small children copy each other and if one goes to the toilet, then others who don't really need to go will follow, and it can be disruptive, as a teacher I see all of these things happening. But I also remember what it was like needing to go to the toilet when the teacher won't let me, how I coudn't concentrate and I waited what seemed like an eternity for the bell to go for break, how I needed to go during break, but there were other noisy kids in there and I didn't want to go when they were there and so I missed the opportunity and got really desperate during the lesson, and I know that it can cause both psychological problems and medical issues. If you've go to go, you've got to go! Teachers need to keep in mind all these things when managing the class and find a solution or compromise.