Getting my music off of my wife’s iTunes account

There’s no means to transfer purchased music from one Apple ID to another, nor Apple Music subscription music.

That content is tied to the Apple ID.

Your own music can be exported, or can be burned to CD media.

If you’re using iTunes on a Mac or Windows, you can transfer the library:

Mac: Move your iTunes library to another computer - Apple Support

Windows: Move your iTunes library to another computer - Apple Support

Or you re-load the music from the source.

Family Sharing can be configured to allow access to music of other members, too.

Family Sharing links.

Family Sharing.         

Family Sharing - Set up.       

Family Sharing -What types of content can I share?