My Gf And I Had Unprotected Sex And She Is

My gf and i had unprotected sex and she is on prescribed medication of dronis 20 for cyst..she completed one full cycle of 24 days with a 4 day gap in between and will end her second cycle today and then 4 days gap. we had sex 2 days ago i.e. on 6th and her periods ended on 3rd....is there any chances that she may get pregnant during the 4 days while she is skipping the dronis 20 as prescribed? and if yes then what are the other measures we can take to prevent pregnancy? please help