What to do about this girl...

Ok this girl at my school is REALLY getting to me. She’s starting to annoy me a lot. She’s the same girl from a few months ago who thought you could get pregnant or lose your virginity from humping random things like a pillow. Now she’s at it AGAIN. Me and my friend were talking about our periods she has irregular ones too so we were just discussing that, and this girl was listening into our conversation and started saying I was pregnant. Now I’m afraid she’ll tell other people that and they’re going to think I really AM pregnant! What do I do about this weirdo!? How do I explain to her that 1. you can’t get pregnant from humping random things and 2. just because you have irregular periods DOESN’T make you pregnant?! She is REALLY getting on my nerves so any help is VERY apperciated.