Can she get pregnant if we had unprotected sex during her first menstrual?

Unlikely: Women are most fertile around 14 days before they start their period. This is ovulation. Sperm can live in the uterus for a few days so she can actually get pregnant from having sex before or after her ovulation. Use condoms at a minimum. If she can use protection as well then you are more covered but she can still get preg with that. If you don't want a baby. Abstinence.