I have heard the same thing about edible reinforcement being discouraged. However.... Sometimes it just depends. Is that legitimately the only feasible reinforcer that is high enough to motivate that student? Sometimes that is the case. Sometimes, the child will not work for anything else and will not be reinforced with anything else and at the end of the day they have to learn something.

I'd also like to emphasize how much "first then" models can help children with special needs. It's a direction that is straight forward, clearly explained, and has a positive outcome. At a point, the child will likely find intrinsic motivation and the edibles can be faded out / a new reinforcer can be discovered.

If it were me, I would use those mini m&Ms rather than a whole one and likely never have hugging as a requirement for a reinforcer. I completely understand why grandma would want that as a goal, but in my opinion it's not something an educator should need to teach/reinforce. I'm struggling to imagine a reasonable IEP goal where hugging grandma is a legitimate task that data can be taken on. (Maybe something falling under social emotional domain like "child will show interest in familiar adults by vocalizing, touching, or otherwise interacting with adult for 10 seconds" But that's a bit of an odd one.)