I think that's an excellent point. Motivation.
Putting aside the ID factor for a moment, there is also the motivation/desire to do something. If it's something she doesn't like doing or has no interest in doing, then she drags her feet, she resists, she fidgets, she stims, she fusses... then eventually does it and has to be kept on task etc. Whereas if it's something she really likes & enjoys, the moment you say it to her she is ON it.
While intellectual ability and comprehension skills play their parts (no one is disputing that), I think that a decent amount of the time she is resisting because she doesn't feel like doing what is being asked of her. She's non-verbal so she can't say "I don't want to put the dishes away.", but she shows it in other ways.
I also think she is extremely prompt dependent from the Massives fcking up doing ABA with her (along with fcking up many other things). I remember back at the old house, Miss Brandy was trying to work with Abbie (and A&P) to move away from and prevent prompt dependency. But, because Asshat decided he knows better and refused to do what Brandy instructed, we have what we have now - total prompt dependency.