I really dont think you can go wrong the a TT600 for a starter bike. Most of the newer 600cc bikes have plenty of power to grow into, they are also light and easy to handle. As you know, just respect the power, my god allot of them are making close to 100hp at the rear wheel. I like the TT600, the handling is first rate and the new 02' models are getting there due in the press. I borrowed one last year for a couple hours and really enjoyed it. It felt like a feather compared to my ST. good luck!
I always want to see others join in and ride and better yet do it on a Triumph but when it comes to new riders I think a season spent on something more docile than a 600 supersport is best. A standard would be a good bet, no plastic, cheaper to fix if it should get in a spill. A GS Suzuki, and Honda Hawk GT or if the look of a sportbike is a must a Ninja 500. Get a solid year under the wheels and then go for that TT.
I also recommend a more cautious approach here. Up to around 8,000 rpm the power of the TT is pretty docile, but above that it can get a beginner in trouble. With this in mind, can she get some seat time on a smaller bike for a few weeks at least? It's too bad there isn't a throttle stop or adjustable rev limiter you could put on the bike until she gets familiar with it. Anybody know of something like that?
I don't recommend any fully faired motorcycle as a first bike. Dropping the bike in your first few months is a virtual innevitability IMO and fairings are really expensive to repair/replace. Everyone I've heard from who has dropped their TT600 has reported a four digit repair bill. Frame sliders would help, but the TT doesn't have a good place to mount sliders without drilling a big hole in the bodywork.
On the plus side, TT600 insurance is a lot cheaper than for Japanese 600s. Also, Triumph actually does offer a throttle restrictor for the TT600. It's in their accessory catalog as a 34PS kit and is available to meet tiered licensing restrictions in the UK. I don't recommend this kit, however. Just tell her not to go crazy with the throttle for a while.