What is the key difference between Sakshi and Durga. The difference is the fact that Sakshi's action whatever they are bad or outright evil stems from her love for her son. Her love for Shaurya is the driving force behind her actions.
Coming to Durga the drive behind her actions is the hatred for Goenka's. In other words her hatred for Sakshi outweights her love for Payal.
In any battle when love clashes with hatred the final victory only goes to love. Because it is believed that power of love anyday is much stronger than the power of hatred.
Sakshi's love for Shaurya makes her instincts sharper. She is able to observe everything around. Every person, every movement and makes plan so that Shaurya can be protected. She doesn't spare anyone or anything that comes near her dear son.
Whereas Durga hatred for Sakshi limits her view only to Shaurya and she ignores the other things happening around her. She is unable to take clues as she is only concerned about having power over Shaurya to corner Sakshi.
If her love for Payal had outweighed her hatred for Sakshi she would have differently looked around. If Sakshi closed the door to Shaurya she would have tried to open another door to get Payal justice. She has taken it as a personal battle against Sakshi, whereas Sakshi actually doesn't have anything personal against Durga. She is doing what she always does. Protect her son. If anyone comes near Shaurya she will react, react with all the venom.
Durga will go on failing if she doesn't understand this basic principle. Her love for Payal has to to outweigh her hatred for Sakshi if she needs to stand a chance against Sakshi.