Chandani was Nahar's ex-wife. She only married Nahar because she wanted to join the family to be close to Brijesh. She was obssessed with Brijesh.
Out of jealousy, she attacked Tara when she found out that Tara was pregnant. In this incident, she fell to the edge of a cliff. While everybody when to take Tara to the hospital, Kuku kaki stayed back to help Chandani. Instead of helping her to come back up, she stepped on her hands to let her fall. Kuku Kaki wanted Nahar to marry a girl of her choice so she can keep the money to herself. Apparently, her husband gave all of his money to Nahar and Brijesh instead of giving to his own son. Therefore, to obtain all the money, she decided to kill Chandani so Nahar would remarry. She didn't like Saloni because Nahar married Saloni without informing Kuku Kaki.
I hope that helps.