There are many reasons why a woman can miss her periods,So maybe she needs to consult another gyna or at least go to a hospital like Marie Stopes or Nairobi Womens that deal specifically with Women reproductive issues.
Use of certain contraceptives like the implant(No-plant) or the syringe(depo) leads to totally missing periods for the duration you're on the contraceptive or having very irregular periods.
My point...if she's not on any contraceptive,advice her to consult a different gyna or visit the above mentioned hospitals for a thorugh check up. Tell her not to panic...it happens. All the best!
Advice is what we ask for when we already know the answer but wish we didn't..
Nevermind what haters say, ignore them til they fade away - Just live your life