i'm not sure if you really mean the knee itself is dislocating or if it is the kneecap. big difference. obviously it is not normal for anyone's knee to dislocate -- certainly not three times in a single year. possible explanations for this would include trauma or orthopedic abnormalities. your best bet is to consult a pediatric orthopedic specialist. he or she can examine the child perform some imaging studies (like x-ray or mri) and suggest ways to treat the problem. repeatedly dislocating a joint can cause many other issues later in life including arthritis and ligament problems. you should not allow this situation to continue without getting a medical expert involved. wishing you well!
why would a girl age 13 knee keep dislocating? it has happen 3 time in a year.