Probably 2 chances why Dadi hate Khushi. Rather than Shyam personally convinced dadi. Shyam would have sent an Anonymous letter to dadi about what is happening in RM.
First Reason: Shyam is such a d**k he will never do anything straightly. He always do things under the covers. He could have hinted that a servant trapped her Grandson and She is such a characterless women like that. May be he could have hinted that the Son in law of the house was thrown out of the house.
Second Reason: Khushi would have resembled like some one in the past. You remember though she assumed her as a servent at first she gave a second look (a strong stare to her). It really have more meaning. And today nani (being our representative) specifically asked the question to her why she hates Khushi without any reason. ( This is the million dollar question in everyone's mind)
Note nani: Pls ask that women to clarify things to you. You have all rights and more rights as you were there during the though times. Also tell her the truth. If incase she is very adament and doing the same thing send her back to the Ashram. Bcoz you keep the RM at peace. She is a tantrum thrower casing problems in the house now only things are getting better in RM.