Hi
I should so be doing homework right now. Or working, since I'm at work.
I think that with regard to mix issues, I can't be of any help, but with the singing...I would say your wife might want to break up the phrasing a little bit. It has a very regimented vocal feeling, almost robotic. I've always been a fan of laying back a little with respect to phrasing and tempo. That is what my style is, definitely, but I think it could help on this song, tho. I also think that this might be a workaround with the comments about repetition. Have her break it up a bit, lay behind the tempo some even. Do little vocal riffs every once in awhile so the last verse is a bit different than the one before it.
I don't know if this will get you anything near a classic rock vocal sound. Any reference to look at? Specific song sounds you had in mind?
Let her work with it a little and find her own voice within the song. If she wants to, maybe when no one's around. This is often hard to do and feel comfortable about letting someone hear the difference you've just made. Opens you up to a whole new can of criticism. Maybe some extra personality will come out in it. This, on top of any eq stuff you might change (but that I know nothing about) might be just the ticket.
I know that when my old band would give me songs that were already written, that is what I would do with them. Just play them again and again, and ask for an instrumental only version as well as one with words, and I would just re-sing over and over, until I discovered my natural melodic tendencies coming out and I could then finally make it mine. That is ultimately the only thing that would bring it all home. They seemed pretty happy with that. But basically, musically speaking, it's the only instrument I know how to play, so why not re-work the phrasing, or slightly alter the melody to be more lax, to fit my instrument?
Have a great day.