I know I sound crazy but really if you stop & really think about it, it really makes perfect sense. Jyoti is Durga's best friend & her worst enemy(next to herself that is)
1. Jyoti is Durga's #1 confidant & there isn't much that Durga has done Jyoti doesn't know about.
2. Durga has done dirt to all of her kids & her 1st born grandchild- for me that was the worst & dirtiest thing she could do at the time using baby Simran, the last vestige of Veena life not only against Raji but the whole family.
3. If Jyoti ever found out that Durga betrayed her in any kind of way can you imagine the explosion from that? It would make the blast at the Maholtra's house look like child's play fireworks. Jyoti has enough information & dirt to not only make everyone hate Durga to death but to get her kick out of the house forever. Full exposure would ruin Durga's life forever!!
I hope all that happens sooner than later.