Can a girl get pregnant the day before her period but she still gets her period the next day?

Unlikley: While all things are possible, not all things are probable. If your periods are regular and it came on time, then having sex the day before is unlikely to result in pregnancy.

Possible: Pregnancy has been documented from unprotected intercourse on any day of a woman's cycle, including during menses. It is unlikely in someone with regular predictable & regular cycles & more so for those with an irregular pattern, but it is possible. If you want to avoid pregnancy you need to use BC for any exposure.