My girlfriend has an iPhone, and she is using Spotify free thingy
I'm using Jellyfin and very very happy (except my favorite client is unmaintained)
I suggested her that I can download all the music she might ever need, she said cool. But also, in case if she needs to find something rare or listen just one time, etc, what options can I setup for her(with no ads, and other bs)
There is no free ad free Spotify on IOS to my knowledge. I recommend Brave browser for ad free YT/YTM/Soundcloud with offline playback. Or Yattee for just YouTube. Another option is the Swisscows search engine which has a integrated ad free music (probably also uses ytm)
Spotify is all music on the go. Certainly for albums or music you want to keep on your device, it's the arrs, but for music, especially playlists, you listen to on the fly, Spotify is a better experience.