Sexual intercourse with girlfriend while she's on her period and she also took plan B pill

I had unprotected sexual intercourse with my gf while she was on her period on 9-8. She continued to have her period normally for 2 more days, so on 9-10/9-11 ish her bleeding stopped. On 9-13 she kept on thinking the worse so we got a plan b that day. Now yesterday she had light bleeding which she described as a pinkish color, and she then described that it turned into dark bleeding with a bright red color and then finished the day with light bleeding again. Is this because of the plan b or is she possibly pregnant? Please any help is appreciated.