Dear Ms Sneha,
In case you are serious about getting back the necklace then you must lodge an FIR with the local police station in writing. During preliminary enquiry the police will ask you about any suspicion on any one. At that point you may name the relative who was wearing it. You don't have to say she stole it but simply that you have doubts because if you say she stole it and later it comes out to be false or you are not able to prove that you had reasonable belief about that necklace being your mother's then relative may file a defamation case. Remember defamation in India is still a criminal offence.
You in query means "Your mother". I used 'you' so as to talk in first person.
Shubham Bhardwaj (Advocate)
District & Session Court, Chandigarh
Punjab & Haryana High Court, At Chandigarh
Disclaimer:- The opinion is only for guidance.