With the stories about data from period tracking apps being shared with law enforcement, I was wondering if there was a self hosted alternative I could host for my daughter. My searches so far have not returned any good results. Thanks!
I wrote a period app for my partner, everything is encrypted and never leaves the device.
It has a option where you can set false passwords, so that if you are being compelled to unlock it, it will get up fake data.
Code is open source: https://github.com/cameroncros/PrivatePeriodTracker
https://play.google.com/store/apps/details?id=com.cross.privateperiodtracker
It may not meet your needs, but perhaps worth a look. I am open to adding features (except for ads and tracking obviously).
(I have posted this before, but with an inappropriate account)