Breasts can have growing pains just like joints or bones, so maybe that is what she is feeling if she is starting puberty.  These pains can be scary.  You'll want to take her to the doctor so you can find out for sure what the pain is.  Once you and your daughter know what is causing the pain, the panic attacks may go away.  I've had a problem called costochondritis, an inflammation of the cartilage in the ribs. Costochondritis can cause chest pains similar to a heart attack.  I don't know how often children have this, but I had a neighbor whose teen daughter did.  Obviously, only a doctor can say diagnose this problem, but my guess is that it will not be dangerous.