For a remote nontechnical user, coaching them through installing a Tailscale client that registers to your account seems pretty accessible.
If you can get on a screen share with her through something like Signal desktop, then walking her through the steps and pasting a WG key in chat might not be so bad.
I suggest using a client that is easy for her to update without requiring a call. Another point for Tailscale I think.
It does in the version I am using
Echoing the base principle I see in other comments: proactively limit what can land in your inbox. I have a rule in Fastmail that only mail from senders in my contacts gets to inbox. If no rules apply, mail ends up in the firewall folder, which I check periodically.
I've been on a big unsubscribe wave for newsletters and notifications that I had previously opted into. If I haven't been reading them within a week, they get dropped. Next step is to resume use of RSS for the topics I want to periodically check up on instead of crowding my email.
The other base principle is to segregate email addresses for personal correspondence and interactions with companies/services/accounts. I've not been good about that out of laziness. That's more about data privacy and while most of my FnF still use gmail it is moot.
I've been a satisfied customer of Fastmail for several years. Based in Australia. Great features for email aliases, folders, and rules.
I fear this is no longer true. Technology has trivialized the cost to surveil a country's population. The U.S. will endlessly fund doing so.