1. The sale deed has been registered in favour of her name with her earlier husband's surname.
2. She should now execute an affidavit before a 1st class Judicial Magistrate affirming that after her divorce fromk her 1st wife and marriage with yourself, her surname has got changed which are required to be reflected in all her documents/papers etc.and she should be named with her current surname.
3. Thereafter she should publish the gist of the affidavit in local Newspaper for public viewing.
4. After completion of all the above steps she will be known with your surname and she with her earlier surname and she with her current surname will be considered as the same person legally.
5. While selling or dealing with her flat, she can write her name with her current surname (though the sale deed mentions her earlier surname) which will be accepted by the Registrar.