Is there real people who are actually that ‘naive’ Or is she just stupid ?

I’d say yes. More due to their feelings of entitlement, rather than their lack of brain matter. Nicola had enough smarts to realize that she was about to spill too many secrets at the tea party. But because of her spoiled and entitled nature, and having looked down on Lass for so long, she didn’t see revealing Lass’ lineage as a problem (especially since I don’t think she knew the Emperor himself was a bastard child)

unfortunately some people are that stupid