I'm also guessing that your school district has a policy that schools HAVE to follow up on kids who have a certain number of unexcused absences by this time of year. Schools systems know there's a huge correlation between consistent attendance and academic performance, so they are make a big deal out of the attendance thing now.
Just go in there and assure the social worker that you understand how important attendance is, and that this was a sort of unusual situation. Make her understand that you take school VERY seriously and that you're a conscientious, involved parent. She'll give you the speech she's required to give, check you off her list, and then move on.