I read the wonderful comments of all.
The thing is it's illogical what they are showing. If Nayan and Brinda fought against each other to kill/save Dev, then the CVs should't say that they will become a naagin after their 25th birthday. Let's say they got half power before the 25th birthday then how come Brinda could save Dev and then later not even understand what happened with her and be unaware of her beeing a naagin ?
Only Manyata could be one of the naagins because she is cursed since more than 25 years. So possibility she got her powers back some time ago or at least 9 months ago. So they can't also make her say that she just got her naagin form back last night.
I can understand bloopers when the show is in the middle but having from the first episode itself it is like taking the viewers for granted.