I hadn't so much as touched a bike since I was 12 when I met my boyfriend the cycling fanatic. For me it was a mixture of the timing, ie wanting to do things with him early in the relationship, and also my being in awe of his abilities, I wanted to try it myself. He got me a very good starter road bike for my birthday, and a very comfy women's seat, an Oasis. Comfort is HUGELY important to sticking with this. And yes, don't make it a hill mashing session or she will probably get turned off. We just started with very short distances, and built from there. I never needed a particular destination on the bike, but a good dinner out afterwards is an excellent motivator!
What made all the difference was he kept me going by telling me how proud he was of every improvement I made on the bike (he's even got a brag thread in the road forums section!

), giving me big hugs at the top of hills etc. It was very encouraging and eventually I just got more and more interested in cycling. Now we are already talking about upgrading me to a better bike!