Originally posted by: AreYaar
It was gradual initially and then they pulled the trigger after 200 epis to be more overt about it.
Malini was always insecure of Imlie and satisfied her ego by treating Imlie like a charity project....Imlie was so obviously poor in appearance as compared to Malini that Malini felt comfortable playing the role of benefactor who was trying to help a girl who was less fortunate than her....but she was always shown feeling jealous/insecure whenever Imlie was praised by Adi or others....then her real colors used to shine through briefly but all in all this was covered up for around 200 epis in the story.....they showed Malini attempting to "sacrifice" after learning the truth that Adilie were married first and technically she came second....so she cooked up a story of having a lover and it was portrayed to the audience that she did this so that Adilie don't feel guilty about causing her pain and can reunite....she also made a show of supposedly trying to get Adi's family to accept Imlie but otherwise enjoyed the family still continuing to consider her their valid bahu.....it was layered and more complex than Jhanak ka ham-handed approach 
Anyways, long story short, Malini suddenly flipped after she saw Imlie starting to assimilate into the family and her mom was always in her ear telling her that no one is valuing your sacrifice and you left your rights for a maid blah blah....so suddenly Malini was shown claiming she will fight her "haq ki ladaai" and get Adi back....that's when she officially started her planning/plotting mode which then continued for the rest of her time in the show....they didn't alternately flip her every other day and she stuck to her evil expressions from that point onwards even as she did the usual vamp thing about gaslighting the leads and portraying herself victim.
Main difference is that leads never treated their shaadi as EMA in that story.....neither ML nor FL accepted any characterization of FL being third wheel.....Adi ki integrity wasn't constantly uchhaloed like Ani's is.....Malini blamed Adi, manipulated him, yes but she still gave him relatively more respect than Arshi has ever shown for Ani. She guilt tripped him but didn't treat him like a slave as Arshi does with Ani. On the flip side, Adi never did cheer phaad of Malini like Ani gets to do of cheap Arshi didi from time to time thoda bahut
1.4k