HI, Welcome to HCM, I am Dr. Das
First of all, dont panic. It is nothing but irregular menstruation
. Even i think that she will have her period in 1-2 days.
If period does not occur in 1-2 days consult a gynaecologist for progesterone
trial which will lead to period and after which your girlfriend have to take oral contraceptive
pillsss for 2-3 cycles for regularization of periodss.
One more thing do an USG of whole abddomen to rule out any chane of polycystic ovary.