14 years old, and didn't have her first period. had stomach ache and brown discharge. is that her first period?but from then she didn't have it again.

Maybe: It may have been the beginning of her periods, however, It is not uncommon for young girls to "stop & start" initially as they are usually anovulatory for the first year or so. If nothing occurs in 6 months have her see a MD to check on the rest of her adolescent development and to be certain that there are no other interfering medical problems such as thyroid disorders to her period resumption.