Ideas to potty train an autistic child?

I am a therapist with an autistic child. She does pretty good with going pee on the potty but hasn't pooped on it yet. She use to request saying she had to go potty and would go but she wont even do that anymore. When she has accidents she is changed in the bathroom. We make potty time fun with toys, books, songs. After going potty she gets a sticker to put on the paper on the wall and she gets a special treat it was marshmallows now this week we started with m&m's. If she goes poop on the potty she gets icecream. We have also made videos on the ipad using olaf and showing her to poop or go potty in the toilet and the excitement we have and the treat he gets if he does it. But she is slipping and not requesting the bathroom anymore or going poop at all yet it's been over 6 months of training her. She is 4 1/2 years old any suggestions?

Read more: Ideas to potty train an autistic child?