I would suggest taking to a shop or two with good inventory (REI, Gregg's, Performance etc.) and have her tes ride a few bikes. Buring a first bike online is a bit of a crap shoot. A lot of these shops often have a few last year's models that you can get at a discount. REI is always having sales, I'm not sure if you get the 10% dividend on all bikes but most likely on their own Novarra line.
There is a difference in "women's" bikes. Women have different geometry needs for how the bikes are set up so a men's bike might not fit as well. Also the saddles will be different and the brake levers are typically shorter to accomodate smaller hands.