My advice is do not choose for her. Let her and only her choose.
Story time...
My friend's wife wanted a minivelo, so as a surprise he went off to get her a bike. Now sadly he believed it wasn't what she should use and he believed the local Trek shop was his best option.
He got excited in the shop and bought two Trek Marlins, as he thought it would look cute riding together on weekends. He even had the shop swap out the tyres to road tyres. Great hey?
WRONG!!
He took the bikes home and a huge fight developed. The bike was put in the spare bedroom, and he was sent off to buy the bike SHE wanted. After a year the Marlin was still sitting in the room untouched.
Now lucky for me, I was after a nice bike for commuting and trails. As she hated the sight of this bike, she told him to give it to me free of charge.
So beware, relying on instinct and forum advice, could be an expensive mistake.