One aspect of your description that is striking is not just that your student is incontinent, but also that she appears to be engaging some pretty inappropriate behavior in conjunction with the incontinence (disrobing, yelling, etc.). The incontinence and the inappropriate behavior may or may not be related to one another, but both seem important to address. If the two are related to one another, then it is possible that both the incontinence and the other inappropriate behavior serve a similar function – perhaps to access attention, or to avoid activities she does not like. If that is the case, then your success with toilet training will also hinge on you and your fellow teachers re-arranging her environment so that she can access what she needs (be it attention, help or breaks from work, etc.) via appropriate behavior instead of the current inappropriate behavior. Toilet training in isolation may not be enough to address the problem - you likely will need specific advice on how to determine why she is engaging the behavior and how to treat the problem.
There are several books available that provide step-by-step advice on toilet training in this population (“Toilet training in less than a Day” by Nate Azrin and Richard Foxx is one example) that may provide some useful tips. However, given the additional problem behaviors the child is exhibiting, I suggest that you contact a local Certified Behavior Analyst for more exact advice. The BACB website has a local service provider directory at:
http://www.bacb.com/consum_frame.html
I presume that the family has already done so, but you might want to recommend that they take her to see the pediatrician to rule out any possible medical issues. Although it sounds as though the problem has been going on for quite some time now, it’s always best to rule out a medical cause when dealing with incontinence.
Best of luck to you all.
I would also add that any approach has to be flexible and yet consistent. If the school is being totally unflexible then they are exhibiting autistic behaviour themselves! There has to be a starting point. What evidence is there that total removal of diapers will cause this student to learn sooner?
You don't say how old the student is.
If she was toilet trained up until 3 years ago, something must have happened for her to regress. It might have been to do with generalisation. Those with autism can learn how to do things in one environment, with the same person, with the same prompts. But if the environment, person or prompts change then they don't recognise the situation as being the same. So, for example, a child may learn to tie their shoelaces at home, but be unable to do the same task at school.
However she is now in the routine of wearing diapers. But I would suggest that however you approach it that she first learns the process explicitly with one person and that once it is learnt that it is slowly generalised out to other people or prompts or environments otherwise she could easily lose the skill again.
Is there any reason to suspect her medications (if any), could be behind this?
Does she have sensory issues? Could she becoming too stimulated or too focused on something that she doesn't recognise the need for the toilet?