Hi: I am an endocrinologist
. Having hair in the armpit could be a sign of puberty. May i know whether she has any pubic hair and breast development. Also when did you attain menarche
. It is definitly a concern because if it is a early puberty, she may attain menarche earlier and height will be low. Get her Xray for bone age, Thyroid functions, LH, FSH, Estradiol
, DHEAS and prolactin
. If things are fine we will periodically follow her and any thing abnormal we will treat her. Get an opinion from your local endocrinologist.