Is the travel router at her place? It needs to be. I don’t think Netbird/Tailscale work backwards like that. If you have access to a Raspberry Pi or just an extra computer you can leave at her place, you can run netbird and use socat to forward the port to that computer so her tv can access it. You wouldn’t even need the router.

I love it. Use it for shared shopping list with my wife.

https://vikunja.io/docs/cli/ Also it supports webdav so you can use it however you like.

Use the tasks.org app and webdav to connect to vikunja. Works really well.