Hi,
Thanks for posting in HCM.
I understand your concern.
Chances of becoming pregnant by
non-penetrative sex is extremely low. However, in your case, since you have ejaculated on her vagina, the possibility of causing
pregnancy is higher in case the semen has entered inside her vagina. But since you did the act just before her periods, which is not during the fertile days, again the possibility appears to be less.
However, she needs to get her periods after the act, either early or late, after the act to say she has not conceived.
Next time, take proper precautions so that such accidental pregnancies could be avoided.
Hope the information provided would be helpful.
All the best.