Suvi, I don't know if there is a trigger in her past. There is something in her past that she wants to bury for sure. Her possessiveness have been shown from the initial episodes. But the extent to which it has come out now is because of the depth in Dev - Sona relationship. She knows deep down that Sona have understood Dev more deeply and substantially. She knows Dev worships her but as much as she enjoys that it restricts her from enjoying a normal or human life where you are not judged for your faults because the basis of your relationship is love and not devotion. She envies Sona having that with Dev. She must decide first if she wants to be his God or his mother who is a human with her own share of faults. Because whatever she is doing now is to get her image back infront of Dev and Mamaji.