I'm going to suggest a slightly different approach here. Please don't misunderstand my post to be critical of your actions. I realize that you are working under school district policies and procedures that require exclusion of students with live lice and/or nits, and that also require checks of classmates. I do not excuse the mother's abusive conduct in any way. But I believe that your district's policies may have fueled the entire unpleasant mess.
Children with head lice pose absolutely no public health threat in the day school setting. Lice do not cause illness, nor are they easily transmitted by normal classmate-to classmate contact. I am not aware of any reputable public health agency that continues to recommend excluding students for nits, or even live lice, except in the situation that the student is so bothered by itching as to be unable to participate in learning. Exclusion policies only address the psychological comfort and convenience of school staff and quell vocal parents who perceive a threat that doesn't exist. Meanwhile, a child loses valuable educational time and parents lose vital work hours to address a problem that is virtually impossible to fully eradicate over night, meaning multiple days of absences for both parent and child. I understand their frustration, although again, that doesn't justify abusive behavior.
While not a quick solution, I strongly advocate working to change district policy. If we expect our students to learn the scientific basis of their lessons, to cite authoritative sources to support their ideas, and to apply sound reasoning in decision making, then we must do so first, as an example. Excluding students because that's what has always been done falls far short. Secondly, we are typically the sole health care/public health "experts" in our buildings or districts, and as such must challenge the educational administrators when they attempt to enforce policies and procedures that are contrary to scientific and public health principles. As I have reminded a few people, they hired me for this expertise. They can either follow my advice, or sign their own names to the directives that I know to be faulty. (That one usually gets them
). Lastly, hit them in the pocketbook. Most states fund school districts at least in part based upon average daily attendance. If nothing else works, remind your well-meaning, but mis-guided leadership that excluding students unnecessarily for head lice is costing them money. Your time is valuable also, and could be far better spent in any number of ways rather than checking a class-ful of heads every time a nit or louse is found. If you had been free to devote that hour to the affected student and her mom, I suspect that your day might have gone a little better.
I realize that change takes time. Perhaps you can make some incremental changes that won't seem so shocking to the staff and parents. If you were able to notify a parent of a suspected lice infestation, but send the child home at the end of the day, that might be a step toward promoting good-will with the parents, who almost never react well. Mom and dad don't lose a day's work, and can address the problem that evening. You can have printed information available for them. If they choose to utilize a hair stylist to assist in removing nits, I applaud them. Sectioning a thick head-ful of hair takes incredible patience and time, and hair care professionals are well-suited to this tedious work.
Finally, to address the mother's abusive treatment: I just don't take it. I learned decades ago in the in-patient setting not to put up with abuse from anyone. I will calmly state once, "I will be happy to continue this conversation when you are able to address me respectfully." Then I hang up or walk away. I liken her behavior to that of a toddler's temper tantrum. No amount of discussion will get thru, so don't waste your time, or give her the satisfaction of commanding your attention.
I'm sorry you had to endure this.