Welcome to HCM.
I have gone through your query. she is almost one month late for hr periods. So, the possibility has to be ruled out first by getting an Urine pregnancy
test done. Urine pregnancy test can be done at home and the kits are freely available in the market. A positive urine test is suggestive of pregnancy. Post coital pills have a failure rate of 1.6-3.5% . So, it could be possible that the pill failed in hr case
At times Post coital contraceptive
pill can also cause delay in periods.
Finally i would say first rule out pregnancy by doing urine pregnancy test and if that turns negative then go for ultrasound
to rule out other causes of delayed period. If the test comes positive for pregnancy and if you dont want to continue the pregnancy then see a gynaecologist for gtting aborted( Dont worry. Medicines are available in tablet form for abortion
but are strictly supposed to be taken only after consulting a gynaecologist) .Be careful next time and use Barrier method ( Condoms)
Hope you got my point.
Wish you a healthy life.