Google knows more about periods than my mom

My mom said that you get your first period when you have sexual relations with someone. So I've figured the blood must be from the vagina covering breaking. And then it rebuilds itself and then breaks again every month, because the new covering is weaker than the original covering. I know that because I'm a virgin and I never had a period.
But Google says that a period is from the egg breaking after getting released from the ovaries, and that you can have a period without having sex. Guys, is my whole life a lie?