Thanks for writing to DoctorSpring.com with your health concern.
The probability of her falling pregnant depends on the time of her menstrual cycle. Around ovulation ( middle of the cycle ) chances are highest.
Right now, the safest option is to take emergency contraceptive pills ( Postinor, Plan B ) etc which are commonly available , and are most effective when taken within 72 hours of unprotected sex, earlier the better.
All the best.
Please feel free to discuss further.