marriage

I get my sister back to home after 5 days of her marriage for rituals. Her in-laws have to come after 2-3 days to take her back. but now it's almost 25 days they are not ready to take her back. They even doesn't bother about her. marriage is done according to Hindu rituals and still doesn't registered because her in-laws not ready for registration. Now what action can be taken and what can we do?