Responses
I talk about it in my post, but in the early chapters, she thought about how great it is to have the duke power - red flag. she told him not to stop the snack girl despite they have enough about her, not cause she is nice, but cause she enjoys her suffering - red flag.
she was thinking that she wants to turn him into a submissive man (other words a toy/dog) so he belongs to her only - big big red flag.
Y'all I get that you are frustrated with Adele, in the beginning I was too, but chapter 77 clearly explains why she does what she does. And shows that she does love the duke and wants to give in. The nobles society is hella hella toxic and if you are on bad terms with them, it can ruin your entire house, reputation, etc. Furthermore, a relationship can't stand forever when all you are getting is negative backlash, rumors about how there is more than meets the eye in your marriage, how the two of you don't love each other and don't forget the fear that some other random lady might swoon in thinking she can destroy the marriage and take the duke for herself.
Even if you say, love conquers all, I doubt that is the case where the nobles (especially the ladies) are raised to look down on others that aren't the norm, such as a marriage between a high standing family (the duke) and a mediocre family (adele), and will spread rumors to destroy whatever isn't the norm so they have one rival less or "keep the nobles image high".
So she needs the duke to make a statement and she can't make it herself, as she is too low on society's ladder AND a woman. Women don't do proposals back in the day and if the duke makes a hugh statement with his actions nobody can counter it as he is far higher on society's ladder + friends with the crown prince. If Adele made the statement, people will say that Adele is just seducing the duke and more women will step in trying to take her place.
If you don't think the rumors are bad, they pity Susan of all things. Saying she had to use poison as Adele was stealing her man. Against those rumors, the only thing you can do is make a big statement.
Now, besides all that about how what Adele does is right, she could have told the duke about it a bit more clear and she absolutely didn't need to tease the duke with thinking she had a new man as that indeed has nothing to do with making sure the duke makes the proposal huge