I had a 2003 model for two years, from what I understand the '07 is different only cosmetically. There is a great Z1000 forum at
http://www.riderforums.com/.
Great power, would wheelie with ease and hang with/outrun the modern 600cc sportbikes. However it could also be civil if you wanted it to be; that is to say I only scared myself intentionally and not accidentally. But not so tame as to consider it a beginner's bike, you didn't say how much riding experience she had, but if she has much experience I would say she would be OK.
For comfort on longer rides, a new seat would definitely be a must, as well as a taller windscreen. I only got the windscreen and not the seat, as I rarely rode more than a couple of hours at a time (used primarily for commuting and playing around a little). I recommend the bike to all who ask (I have ridden an FZ1 quite a bit and a ZRX a little, both of which are in the naked category).
Sold her for a song because we were about to have our first child and I thought, erroneously, I had to sell the bike because I wouldn't have time for riding anymore/needed the money/would kill myself if I had a bike. Seems that happens to a lot of guys. The only positive was that my next bike was a Warrior!
Though I'd still love to have the Z when I feel like gettin a little crazy
Good luck with your decision