Is it possible to get pregnant with pre-cum the day before a girls' period? is the chance more likely?

Not likely: Pregnancy occurs most commonly if sperm is introduced in to the female system (precum has sperm) in a 5-7 day time period around the time of ovulation. If it is the day before her period you are out of that range and pregnancy is unlikely. Use condoms if you want to avoid pregnancy and infections.

It happens: Pregnancy has been documented from exposure on any day of a girls cycle, including during menses. That would be more likely in a girl with irregular periods, and most are rarely fertile during the time you mention.Percum has sperm in it, and it only takes one.Unless you want to risk being a dad, use a condom with any intercourse, and cover up before you get started. You may luck out this time.