I agree with everyone else that starting her at the MSF class is the best plan. See if she's into it and then let her pick out a bike.
I really think buying the 250 is not the best choice for most people.
However some people need a small bike. Some new riders are intimidated by larger bikes and the 250 will ease their minds while riding it, and comfort with the machine will encourage progress.
For most people though a 500cc+ cruiser is a good starting point I think. I learned on a Suzuki Marauder 805 and it was perfect. I bought it cheap, dropped it once on a turn, and now I'm selling it and I just bought the bike I really wanted, a 2012 KLR 650.
I'd hate to have dropped the new bike...
"Love is when you feel the same way about a person as you do about your motorcycle."
~Hunter S. Thompson