Answer:
Normally, yes. 'It' happens (should happen) every month. Except if a girl is pregnant.
When a girl gets her period for the first times it can be irregular, but that's normal. Her body still has to get used to the change and produce the right amount of hormones.
The period can be a little irregular, actually it's a cycle of 28 days, so it's never exactly a month until the next one. It normally takes 5 days for a period to be 'over'. Sometimes it can skip a month, but only if the girl is really stressed.
If it suddenly stops, for no apparent reason (no pregnancy or menopause [when a full grown woman, mostly around 45-50, stops getting her period]) there is definitely something wrong. She should go to the doctor then.
I hope I could help.