Sarla is brain washing Devanshi into doing as she bids. She knows it is easy to brain wash a kid - so she is abusing her. She claims she is using Devanshi to expose KS - in reality she is using Devanshi to satiate her never ending greed.
Today when she asked Devanshi to promise to give her 100 earrings - she was not doing to take revenge KS. She was doing it to grab any money that Devanshi may ever have. She had no intention of gifting Devanshi the earrings. She had always intended to give them to Sakshi - and she clearly indicated it to her husband.
Her husband may keep quiet today - but he is definitely troubled by her behavior and some day he will loudly rebel against his wife.
Devanshi is innately good - she does not know what meanness or greed is all about. She will happily try to please Sarla. But her conscience is very well developed - she knows good from bad and will ignore Sarla once she knows that her intentions are bad. Example, she ran to feed the hungry person halwa puri and later on she fed him ladoos - all this was done against Sarla's wishes.
Just as KS is going to have her day of reckoning - Sarla too will have her day of reckoning. Then neither Sakshi, her husband or brother will support her. Sarla will be forced to turn to Devanshi and seek her forgiveness