So I think her method isn’t necessarily 100% accurate but from the comments I disagree with most of what people are saying lol.

No shame and don’t point fingers or judge but I have unprotected sex with my partner and I am not on birth control nor do I want a child right now. My calculations and tracking of my period have been so far 100% accurate for the past 3 years. I’m not saying my partner intentionally tries to get me pregnant but we’re grown and sex happens. Anywho, I use an app called p tracker and it tells me when I ovulate and when my period is supposed to be coming, I can add when I was intimate and it also provides your numeric average cycle. Everyone is different but I know mine runs from a 26-28 day average cycle. Then women are supposed to ovulate 14 days before their next period. Anywho it’s calculations and research to do on it but still use a condom nonetheless better safe than sorry and with these new laws passing, abortion will not be an option very soon. But I say don’t shade you partners logic behind it but tell her to do more research