My gf menstruation just stopped at night? is this like the early pregnancy bleeding?

We're both virgins. We've never done penetration. The only thing we're worrying about is that if my fingers touched my penis before I fingered her. I CAN'T REMEMBER. but she said she tasted precum when she is giving me bj so we are frightened that WHAT IF I TOUCHED MY D*CK WITH PRECUM WITH MY FINGERS BEFORE I FINGERED HER. She was 3 weeks late but today morning she had her period but we are worried now because her period stopped right now at night. She is irregular and she said she had experienced this one day period before.