Can Postinor 2 Cause Early Period?

hello...here, I had sex with my gf on sunday & it was our first experience..we had unprotected sex..she was to have her periods after one week...bt, bcoz we had unprotected sex, i gave her a tablet of "postinor 2"...and yesterday she said me that she started to bleed bt the periods were to come on the next week...is the bleeding due to the tablet?will it b a problem?