If she did not invite an unstable Dev, the engagement could have taken place without hiccups.
She invited him and then blamed him for creating scene. Very good Sona, how easily you found scapegoat?
Not only invited him but throughout watching him only while neglecting Ritwik. She did not prevent the fiaso in time by asking his dada to take care of Dev. She waited until Dev fell down.
And then attended him, took him to his home givng signals that she cared for him. When Dev came with flowers like an excited school kid, she asked him to get lost.
Dev is caught between two hot tempered women.