I have a 14 week old Blue Orpington pullet that has a loud rattle when she breathes and slinges her head occasionally and kind of sneezes. Otherwise, she is perfectly fine. She has done this since she was a chick. She is growing, eating her feed and all the treats. There is no discharge of any kind and the rest of the flock is just fine. What is it and what can I do to help her?? Thank you in advance.