Hi L.,
When a preschool asks that your child be potty trained, that does and should include learning how to wipe. It is difficult for a teacher to stop teaching her other students and go into the bathroom with each child each time they go. Otherwise, there would be no reason to expect the child to be trained as it would be necessary for the teacher to stop teaching and accompany each child to the restroom.
All children, when learning how to wipe, will have some difficulty cleaning themselves properly. This is to be expected. I would suggest when she returns from school that you take her in the bathroom and check her little hiney. Praise her on what a good job she did wiping and just keep reminding her how to do it properly. She will get the hang of it. I keep a box of diaperwipes in my bathroom for such instances. Also, make sure to stress how important it is for her to wash her hands after wiping. I always tell my kids "Let's get those bathroom germies washed off!"
Our pediatrician suggested that until my girls got older, to have them wipe from the front. When I asked about transfering poop from the back to the front, she said not to worry about that (for now) as when they have pooped in their diapers, the poop spreads all over anyway. She said it's more important to teach them to wipe well. They are just not very coordinated at this age and wiping from the back is difficult. Once my girls got a little older, they learned to wipe properly. It was not a difficult transition.
I think if you choose to speak to the Director, your concerns, while important to you, will not change their policy. There is only so much time during the session to teach all of the children all that they need to know and having to stop and help a child in the restroom will interrupt the flow of the classroom.
Good luck!
C.