hi,thanks for query.Normally the age for puberty
is about 11-13 years in girls and 12-14 in boys.This is the time when under the influence of hormones changes in body takes place.At times due to some hormonal
imbalance this can be delayed or come early.8 years is definitely early.It is advisable that you friend should talk to her primary care
physician about this and just see that things are normal.
wishing you good health.