1) She can apply for the legal heirs & Succession certificate in the court and she is entitled for it.
Succession certificate
Usually, a succession certificate is the key document that you need. "In the absence of a will, a succession certificate will be the primary document through which the heirs can stake a claim to the assets of a deceased relative," . A succession certificate, under the Indian Succession Act, is a document that gives authority to the person who obtains it, to represent the deceased for the purpose of collecting debts and securities due to him or payable in his name.
For a succession certificate, you need to apply to a magistrate or a high court. Usually, courts have a separate cell that issues succession certificates. When it comes to immovable property , there are other documents, like, for instance, a gift deed, that can help. "In some states, in cases of intestate succession, property can be gifted or the share in the immovable property can be released by the legal heirs to each other. This can be done by executing and registering the gift deed or release deed with the registrar of assurances."
2) Once she submits the Succession certificate a Society will issued NOC certificate for the estate agency.
3) For applying share certificate and submitting the succession certificate to Society, The Society will published same in the NEWS paper and your mother also published separately Notice of getting Ownership of flat. Than after 15 days the share certificate will get transfer on your mother's name if not received any Objection from any his family member.