I am currently riding my wifes Ninja 250 while my Busa is fixed. (Small traffic accident, not my fault... no really.) This bike is fun. I use it as a commuter right now and am getting roughly 50-65 mpg.
Starter bike or not, I LOVE this bike. It is just lotsa fun! The gearing and throttle are way off from the Busa, duuuh, but for a new rider I think it is perfect. Even after we get her upgraded to a 600cc bike or something like that I will not be selling this Ninja 250, it is a fun little machine.
a couple of downsides:
Keep in mind I have a brand new 2006:
If you follow the break-in you need to keep it under 4k rpm for the first 500 miles. That's 35 miles per hour or less. After that from 500-1000 you keep it under 6k rpm. That is about 40-45.
This bikes runs cold. It takes a bit to warm up, several minutes actually of adjusting the choke to keep it between stalling and going nuclear. It is irritating.
Top speed is about 110 mph but it takes a bit to get there.
All in all I think if your wife has never ridden before this is the perfect bike but she WILL outgrow it in about one season. If she HAS ridden before throw her butt on a 500-600cc cycle. She will get bored/frustrated with the 250 too quickly.
I hope this helps!