Not that this was one of your listed options, but have you considered setting up your own Plex/Jellyfin/Emby server along with the *arrs and adding her to that? You can't get much more snappy and Netflix-like than that.

I can't imagine this would offer a very pleasant viewing experience for a first timer when it relies on stuff like YTS, RARBG (they need to update their page apparently), KAT, EZTV, and TPB. I can see the potential for her to be bombarded with a bunch of fakes and low quality rips.

Can only help with the last point - Nvidia Shield is a beast. I have two of the 2019 Pro and they're just great, nothing comes even close. I've also had the 2017 version and it was great as well. Can't speak for the base model, haven't had a chance to try.

It's a bit of work to set up, but plex/sonarr/radarr/jacket/bazaarr/overseerr/qbitorrent+openvpn is the way to go

I would add real-debrid too it speeds the load time. Regarding the subtitles I think you configure it when installing torrentio. For Android TV I have a Firestick tv 4k and Firestick 4k max, both runs streamio+real-debrid+Torrentio very well. For the French content you can configure it to be priority when installing torrentio

Just wanted to add that you might want to use real-debrid or a VPN, depending on your jurisdiction. Nothing worse than your mom receiving expensive letters. Though I guess it's not a problem since you've been doing it for a while.

My TV setup is:

-Chromecast with Google Tv

-Novaplayer (Netflix like catalog with info parser)

-synology NAS (To store the downloaded content)

How you get the programs in the NAS is up to you, doesn't need to be a NAS

Selfhost Jellyfin