A marriage which has already been solemnised can be registered either under the Hindu Marriage Act, 1955 or under the Special Marriage Act, 1954. Hindu Marriage Act is applicable in cases where both husband and wife are Hindus, Buddhists, Jains or Sikhs or where they have converted into any of these religions. Where either of the husband or wife or both are not Hindus, Buddhists, Jains or Sikhs, the marriage is registered under The Special Marriage Act, 1954.
In your case your daughter converted to islam and married as per Muslim custom.Registration of marriage is a mode of proof of marriage.The Special Marriage Act, 1954 provides for a civil marriage of two Indians, without the necessity of renouncing their respective religion. The Act provide for civil marriage that would enable individuals to get married outside of their respective community mandates, many community based laws did not provide for inter – community or inter – caste marriages. Under the Special Marriage Act, 1954 any ‘two persons’ can perform a marriage. The inter –religious or inter – communal marriages are possible in India only under the Special Marriage Act, 1954. Under the Act a marriage has to be in a civil marriage form, though parties are free to perform any other additional ritual or religious ceremonies if they want to.
So if you would like to do the marriage under HMA act ,No need of divorce . If the groom converted to Hindu his marriage will be null and void. And thereafter they can perform marriage as per Hindu rites and then get the marriage registered under HMA.
Better register their marriage under Special marriage act after conversion.