Protected sex, partner worried that she is pregnant

Patient: My girlfriend, 16, and I(16) had sex and we used condoms. She bled when we did it. She was due to start her period soon, and she says that she is still bleeding a day after the fact. She says it smells like her period blood does but there is not a lot of it like usual and she is scared that it is implantation blood. I don’t think it is but I want to put this to rest. Thank you for any answers.

Symptoms: Lighter bleeding than period