In answer to a few questions raised by posters:
The mom does not work. She puts the child in a morning daycare program so she can "socialize with general ed kids" (her words). Mom picks up the child and transfers her to our program which begins at noon. On many days, she stands in the parking lot and talks to another mom in our program. It's possible she has appointments to get to on some days, but she does not have a job.
This particular child has no physical needs that would preclude the mom from changing her in the back of their minivan.
I do not know whether the daycare changes her right before she leaves. I also don't know if she does her business at the daycare or in the car.
Today, our teacher was prepared to speak with the mom since it happened Mon-Wed this week. But, the dad brought the child to school, which happens on occasion. Dad walked the child to the door, smiled, said hello, then announced that his daughter needed to be changed! The teacher didn't want to say anything at that point since dad rarely brings her. She does plan to talk to the mom next time it happens.
It wouldn't be a huge issue if we didn't have a tight classroom schedule. On some days, kids need to be walked to the speech room as soon as they arrive. She misses the first few minutes of her speech session when she has to be changed.
I should also add that I, myself, am a parent of a special needs child. In fact, he was a student in the very same program 16 years ago before I began working there. I know both sides of the issue. While I knew that my son would be well taken care of while at school, I also respected the staff's time. I never dropped my son off with a dirty diaper.
The teacher is planning to speak with the mom at the next class. I appreciate everyone's input.