Some really good answers, and welcome to the mac side of the fence

I'll just throw a little side info on here... instead of mounting your music share via samba, install mt-daapd on the linux box that contains the music store.

mt-daapd is a streaming music server that speaks iTunes protocol. It will automatically show up as a music source in the left pane of your iTunes window when she's connected to the network (provided she has the option selected to "automatically look for shared music").

Then, whatever music she wants available locally have her just copy the mp3's and import them directly into iTunes via drag and drop. That way all the music she sees is music she has with her. When she's out and about, she selects her own library and sees all her music. When she's connected to the network, she selects the music share and it shows her all that instead.

The added benefit to this is that mt-daapd can be configured to stream unsupoorted formats. That means you have access to normally unsupported formats (such as Ogg Vorbis) transparently within iTunes.

It's a great piece of software. I use it at home to stream to my mac and to my Roku Soundbridge.

-- Gary F.