No adult ever said anything negative about MSA. I think like with schools, workplaces, etc., the set had its cliques and gossip and groups and she didn't fit in with their behavior at the time. Being "different" is always looked at negatively by others many times. I think the fact it was still brought up was mainly to sell the books. I'm sure without being a fly on the wall, they were told, the more inside gossip, the more discord talked about, the juicier it would be. I don't think Michael Landon would have liked it.
Melissa Sue added a lot to the show, her character was central at times and she did a fine job as Mary. Many older actors gave her a lot of kudos and even if her talent was mainly as a child actor, she handled herself well and I'm glad she didn't stoop as low in her rebuttals.