My wife (5ft) started out on a 1988 Honda VFR 250 Interceptor. It was a little smaller than the ninja and already had a few dings and scrapes. She did have a tip over on it once but for the most part she learned without incident. She has since moved up to a Monster 620, and has been looking at the BMW FG650's.
Having been there, I would highly sugest getting a "beater" for her to learn on than investing in something nice right off the bat...but thats just my 2 cents.
