I know this may sound weird. But CT is a practical and sharp woman. Her plan against Diya is not personal. She is clear about her motives. She wants the control over the power.
Considering the royal hierarchy, she won't get to be a queen but she wants to be the King-Maker. A position which is considered to be more powerful than the King himself in politics.
And she has taken right steps. She discredited Diya, and she gained trust of Ratan in the process.
But thanks to Kaku sa who is essentially a stupid and vindictive man, Ratan got the idea of punishing Diya.
She would prefer that they let Diya go away and get the property back while Diya is hurting with the insult.
But Kaku Sa is as immature as Ratan Sa. :-D (To be honest, more so) So he gives a stupid idea to punish and torture her. And Ratan sa who needs to vent out his pain, is doing his bidding (even if it is for a short period)
And THIS is why they both and their immaturity is the blessing in disguise for Diya.