Definitely listen to yzfcathy. On this forum, looking for a bike for a girl, there are plenty of US to get opinions rather than the guys. I am only 5'3", so my opinion will be a little different. BUT, I went from a 1980 Honda 200 standard type bike to a F650GS. It made me nervous, but I took it slow and figured it out. Less than a year later, I rode her to Alaska with my husband, and then went by myself to an off road riding rally type thing. I'm totally hooked, and lets be honest--I ride like a fucking champ.
I think there is nothing wrong with you asking for opinions about what kind of bike to find for your girl. Truly, though, have her sit on a couple different bigger bikes and see what is comfortable, ergonomically speaking. She'll figure out the larger engine.
Btw--Jnich77--Dude, really?. I want to give him the benefit of the doubt, think he is just trying to be funny (and failing miserably), but not sure on that one...
Love is the feeling you get when you like something as much as your motorcycle. Have you ever been in love?
GIRL ON A MOTORBIKE