Hi M.,
All children are different - I'm sure you'll read this a hundred times - it is normal to not be regular for the first year or so. My oldest, now 18 took about 9 - 12 months to become "regular", some months she wouldnt get it at all, others for almost 2 weeks, other months just spotting for a couple days. My 2nd daughter, now 16, didnt get her period until just this past spring, after she turned 16. I told her to count that as a blessing.
Keep her close and keep communications open with her as much as you can. If you feel she is keeping secrets, and her period doesnt come in the next 2 months - take her to the gynocologist to have her checked out.
Good luck