
Usually, I dislike characters with her personality; bubbly, too energetic, naive and too innocent for their own good, a bit on the dumber side. But surprisingly, I actually like her a lot. She's childish but not in a bad way. She is weak but not weak enough to make her pitiable. For short, she's a mess but I like her for that.
And I absolutely adore how sweet and warm her relationship with the prince feels. The prince is also a great character; finally a "cold" ML that doesn't treat the FL like trash at the beginning.
To be honest, this story feels like the POV of a side character from another story. You know, like the isekais where the MC reincarnate as the villain, Solleia in our case, and our princess would be the clingy lover/concubine of the prince. If the story would have been from Solleia's POV, it would have been one of the "reincarnated as the villain" tropes; we would have liked Solleia and disliked the princess.

Don't know about the last point. Most of the villainous stories are about women that aren't that bad in the first place. Only a few are about one's that did something terrible and even they change their ways when they live again etc. What solleia is doing is objectively evil. Moreover unlike the other clingy side characters our MC isn't secretly a bad person. Technically she didn't even take an proper steps harm the villain. Neither is she secretly a bad person like other concubines.

You'll find a better translation from chapter 82 up to 89 here: https://zeroscans.com/comics/28025-the-monster-duchess-and-contract-princess
Sadly, the latest chapters aren't translated. I don't know if the Scanlators dropped the story or if it's just taking them longer to translate it.
They're so lovely