Being naive and a little stupid is not a fault, and it never will be. Taking advantage of naive and stupid people is.
Jeannette is just a little girl trying to be happy and with a family, since up to this point in history she has never had one. She's not particularly smart or clever, but that's not a fault. And above all, she has no defence against outside intrigues and machinations, having always lived inside a golden cage. She is not even comparable to Athy, either because the latter has memories of her past life and a critical adult sense, or because the latter as an imperial princess has received training to detect and counter such deceptions, while the former is so much if she has learned how to embroider, dance and drink tea without making noise.
Accusing one of them for not being as awake as the other is just unfair.