Immovable property in partnership firm

Dear sir, My mother,father and uncle were partners in a partnership firm.The partnership firm purchased an immovable property in the year 2006 via a registered sale deed between the seller and the firm.In the year 2010 my mother retired from the partnership firm via an unregistered retirement deed,giving up her rights in all the assets of the firm.A new partnership deed was made in which the continuing partners took over all the existing assets of the firm.My question is whether the relinquishment of my mother's rights in the immovable property of the firm were needed to be done by a registered document?If no registered document was executed at that time then does my mother still have rights in the immovable property of the firm? Regards