I don't expect most of you to understand this, but I just wanted to clear out some of the actual plots that have been established in the show and not assumptions due to preexisting biases. If we take just the dialogues that have been said in the show and scenes that have been actually shown in the show Ramona is actually correct.
Literally ZERO Luthras other than Rishabh took the humiliation that Karan bestowed on Preeta known as the 'first marriage' acknowledged it as a marriage. Karan and his family vehemently tried to deny the 'second marriage' as well up until the police arrived.
On several separate and specific occasions before getting engaged to Karan, Mahira asked both of them to clarify their relationship status. Both of them kept denying it in front of her. But even more importantly the incidents leading up to Mahira and Karan's engagement were not by any means part of her machinations. It was Sherlyns. In fact up until Mahira got kidnapped by Shrishti during her engagement all her feelings expectations and character traits were genuine and pure.
The Luthras DID give her false hope. Karan DID make fake promises. In Ramona's perspective she was only helping her friend and to a certain extent she was. Her belief was based on the promises and assurances given by the Luthras. It was the Luthras who wanted an alliance with Ramona's daughter. And although we as viewers know that Mahira intentionally pushed Preeta infront of a truck and also Mahesh Uncle from the stairs. But Ramona doesn't know about it. More importantly those incidents were not the reasons behind her wedding being fixed with Karan anyway.
In that aspect Ramona isn't wrong in wanting the Luthra's to be in jail ALL of them. Especially Karan.