What you really need to instill in her is that she needs to learn how to ride the bike good enough so that she can ride without thinking about how to do it.
Until that point you're not safe on the street. If she's thinking, ok, shift, clutch, siganl, ect., that's no good.
She needs to be aware without being scared, yet assume everyone on the road is trying to hit her.
You know yourself that you're focus needs to be on your surroundings, not thinking about how to control the bike.
Most women that I've ever seen learning to ride get caught up in the fun of learning and riding itself(not being disrespectful or trying to stereotype). The only thing wrong about that is that their focus isn't on the car 100yards up the road that might open a door, run the light, or swerve into your lane.
Most women tend to learn by the book, as opposed to us, who tend to read instructions as a last resort
Ladies, I know there are plenty of guys out there riding bikes that have no business even sitting on one either.
You know her best. If you think she's aware enough or that you can make her that way she'll be fine on anything that she's comfortable driving.
I also know several small girls around 5' tall. They've all ridden 4 wheelers with manual clutches. None of them like the clutch because their hands tend to be so small, and the repeated clutch pull is difficult and becomes uncomfortable. That becomes more of a control issue on two wheels too.
Just something else to think about and maybe lean towards the Can Am Spyder.