Could Vaginal Bleeding Be Implantation Bleeding Or Just An Early Period Given Potential Semen Exposure During Sexual Activity?

Hi. So I’m having a bit of a pregnancy scare with my girlfriend. So last month on the 26th, her period began. On the 1st of this month, I had a very very small amount of semen that I might have got on my hand. Now I wiped this off about 5 minutes before if there was any and touched multiple other surfaces with dry hands before fingering. Assuming she has a normal cycle, her next period would be the 23rd. But today, she began bleeding. She thinks it’s her period as of right now but I’m just worried. It should’ve been way before ovulation and I don’t even know if there was any semen in the first place. I’m wondering what the chances are of implantation bleeding and pregnancy vs an early period. This would be a little over a week early.