Miscarriage circumstances ?

My girlfriend of 8 months told me she had a miscarriage on Friday night (5/2 while I was out of town. We were unaware she was pregnant. I was unaware she could get pregnant. She had a tubuligation 2 years ago after her 2nd child was born. She had a ruptured ovarian cyst 2 months ago. She said that maybe the ruptured cyst created a new passage. She had her period 2 weeks prior to the episode on Friday. She said her period wasn't normal. She said she called her OBGYN and was told that she was probably 6 weeks pregnant. She said she took a home pregnancy test and it came back positive. She said the OBGYN prescribe pain medicine and another medicine to help clear things out. I found Hydrocodone and Nitrofurantoin. Could the Nitrofurantoin be used to clear out things after a miscarriage? We had sex on Sunday afternoon and I didn't notice any spotting or anything unusual. I am highly skeptical of all of this. Is it possible that she had a miscarriage under these circumstances?