This sounds like a classic "it's not a technology problem and technology won't solve it" situation. Synchronize by traditional human-to-human communication and

This sounds like a classic "it's not a technology problem and technology won't solve it" situation. Synchronize by traditional human-to-human communication and then you both do your preferred method of self-organization independently. If you want to synchronize schedules asynchronously, a paper calendar on a wall in the house should work for that. If/when you do HASS, make sure that any device that she is affected by (save for the router/hotspot, I guess) can also be controlled and overridden manually with physical buttons without needing her to use a computer or smartphone. If she has any concern about data/privacy which play into this, respect that by self-hosting locally rather than offloading to google calendar et al.