How do kids choose their Favorite Person?

My 4.5 year old has a great bond with my FIL but at the moment her great aunt is her favorite person. She wants to be with her all the time. It seems like kids pick a person all of sudden. Her great aunt was on a 7 week trip. She always has gifts for the kids and she’s so soft spoken and lovely. Do your kids switch favorite people? And do you know why?