Hello there.
I can understand your concern.
As it happened on 27th, considering her cycles are fairly regular, she will be in her infertile period of her cycle. So i do not think she will get
pregnant.
Also, you shouldn't do self medications. Just wait for her periods to come.
They can be delayed a few days. If they don't come, consult a gynaecologist in person for further evaluation and management.
Best regards.
Dr. Anil kumar jain.
Bangalore.