My wife decided last year that she too would like to learn how to ride. I had her covinced that a 250 was perfect for her to learn on. We were, however, fortunate enough to find a vlx 600 deluxe that just came in to the local cycle shop on trade. It proved to be an excellent machine for her to learn on. The very low center of gravity made it remarkably easy for her to handle. She never once laid it down. I had her begin in large parking lots and eventually had her ride ahead of me down some rather isolated roads. She is handling the highways very well now and toying with the idea of buying a new bike this year.
The 250 may prove to be a great starter also but you will grow out of it the intant you take your first ride down the open highway.
Slow is the key to control. You will not learn to ride in one day. If you can control your bike at slow speeds, you will have the ability to safely motor down the highway.

Best of luck,