Chatman wrote that her daughter sought treatment from the "world trusted" former Team USA Gymnastics doctor for many injuries over a three-year period.
Chatman said that Nassar, who seemed a "kind, gentle man," had even offered her daughter after-hours sessions.
"'How nice of him!' we thought. Little did we know that this was a pattern of his behaviour," she wrote.
Chatman became suspicious of Nassar's behaviour after noting her daughter was always covered by a towel, and wearing small running shorts.
"I, unlike others, don't remember him 'blocking' my view, but since she was covered, I was unaware of what he was doing under the sheet," Chatman wrote.
Larry Nassar was sentenced to 40-125 years in prison. Photo / Getty
"After he was done, he washed his hands and I remember thinking, 'Did he just do what I think he did? Where are his gloves?' I immediately dismissed the thoughts as there must have been some good reason. This was Larry after all. No need to question him. I trusted him. We all trusted him."
Chatman's world was rocked in September 2016, after the first report of sexual assault allegations against Nassar were released.
Chatman said she felt "crushing guilt" as she realised what Nassar had done to her daughter in her presence.
"Did I let someone assault my daughter in front of my very eyes? Never would I ever allow that to happen! My children are my world and anyone who knows me, knows that about me. So how could this have happened?" she wrote.
"We, the parents, unknowingly entrusted our most precious daughters to someone, who on the surface looked like a lamb, but was really a wolf in sheep's clothing."
Chatman wrote that none of the parents "knowingly allowed their child to be abused" and that they were "manipulated by Nassar just as their daughters were".
Nassar was accused of sexual assault by more than 250 girls and was sentenced to 40-125 years in prison last month.
