I actually hadn’t replied to your anon yet because I was still thinking about it.
I don’t think she had any preconceived notions about Charles and Camilla, at least regarding the infidelity. I know it’s going to sound strange, so bear with me.
I’m actually re-reading the Google Books excerpts on Morton’s Diana book to try to remember what that book felt like. I know the public outcry over it was what it revealed about Charles’ infidelity, but the book itself is, imo, not about that.
It’s mostly a huge martyr trip for Di and Charles is not even the starring player. It starts with her dad and mom and the divorce and how different that made her feel. There’s a lot of stuff about her siblings and school. I suspect that would be the part that would draw in someone like Meghan. That and the fame and adulation parts.
So I don’t think Meghan would have much of an opinion on Charles other than “oh, cold fish and cold parent and OMG Harry my parents mistreated me too!!!!!!!!” I don’t think she would resent Charles and Camilla for the adultery. That part of the story likely didn’t make much difference to her. The whole “poor mistreated Di became an icon through fashion and charity work” would be the part that appealed to her.