Of course Meghan knew who she was marrying. Even if she didn't quite understand the ins and outs of joining 'the firm' beforehand, this would have been explained thoroughly to her before she married him. Anyone who thinks somebody can marry the son of the heir to the throne, and not go through exhaustive procedures about what is involved, is naive.
I think, like Diana, the reality was very different from the fairy tale. Unlike Diana, Meghan was older, not from the same social class - Diana, lest we forget, was a Lady, who mixed with Royalty from a very young age. Meghan, I think, quickly realised that whilst she wanted the celebrity of being married to a Prince, the downside, the restraints, the protocol, the "duty" was too much.
Diana would have coped with all that Meghan couldn't cope with - the duty, the Royal tours, the protocol. All she wanted was to be loved, and not one part of a "threesome" marriage. I think Harry does indeed love his wife very much, and has given up a lot for her. If Diana had been loved as much by Charles as Meghan is by Harry, she would have been extremely happy with her lot.
Meghan leads Harry by the nose. For how long, remains to be seen.