Ragini has always been very evil, its her plans that have improved a lot. She was after all the one who brought Suraj back to Azadganj. Success increased her confidence and she stopped getting those nervous break downs whenever she fails. How strong is her confidence is yet to be tested. She's also helped by having Ranjana and Vivaan on her side. I hope one day Vivaan pays the price for trusting her.
Ragini was always with KN for her own interest even breaking his orders and sabotaging his plans a couple of times . Once she eliminated the threat of Suraj and made Vivaan under her control, she removed KN from the picture and assumed control. I hope we'll get to see KN's punishment for her because it will be brutal.