I am glad I finally got my wife use this Foss alternative instated of some garbage that sends your data to a proprietary server.
Reminds me very much of: https://yourwife.zip/
What F-droid Version are you using? On the recommended version the downgrade button is still there.
An actually halfway decent idea might be adding a strong UV light inside the washing machine or dryer to kill germs. Modern eco methords with 30-40 C° just dont kill the germs effectively. You’d need to wash your clothes at last at 60C° which most clothes (especially sports wear) cant handle anymore. Or just dry them on the outside where we also have a Strong UV source aka. The sun.
That sounds quite intriguing, I’ll shop around and give you an update!
The App (Drip) gives you after about 3 months acurate times on when the period should start. If you want accurate fertility tracking your girlfriend will have to measure her basal temperature (ar best daily) and either look out for changing cervical mucus or change in cervix opening/hardness.