How much higher are the odds on an antibiodic of getting pregnant while taking birth control? Please Help :(?

My girlfriend uses birth control an takes it like clockwork.. On time every time... right..... But heres the problem... Please follow this it might seem a lil hard to follow so please take this all in.. lol... We had before this happend so remember we had before surgury... She just had her wisdom teeth taken out an they put her on peisellen an i know it weakens birth control.... She is on her last 2 active pills an is suppose to start her period in a few days... But 2 days before surgery we had so she hasnt been taking any antibiodics at that time... 2 days later she has... so what are the chances of her getting pregnant after the fact of ???? I know birht control is not 100% an she is a few days away from her period an took antibiodics after we had ??? Hope you can follow this an tell me the odds?? High or Low... Should i be this scared :( i know im dumb an didnt even think about it at the time :(