One of my friends with six kids who is planning on having at least ten tells people, "We've been called by God to have a large family." People usually don't try to argue with God's calling!
I'm so sorry your sweet little girl had to here the word "slut".
Lots of rude people out there. One lady in a restaurant tried to tell me that I needed a religious parenting book to help me raise my autistic child better. My second child doesn't have autism or behavioral problems, so you'd think she'd figure it out that it isn't the parenting.