How do I convince my girl to start riding?

This is the only really sensible comment in this post.

People have, to a large extent, the ability to exercise freewill. If you're girlfirend wanted to ride a bike I'm sure she would be capable of communicating this fact to you, or whoever else she may feel comfortable discussing it with.

Asking, "How do I make someone do......" demonstrates just how little you think of them.

As for this:
Grow up and fuck off.

haha - you need to chillax Object. Or is it because she works in your building that you're defensive?

You can't deny that the 'urban cowboy fixie rebel adventurer' image isn't particularly appealing to some of the fairer sex, and there are many bikes more instantly appealing to people than the cold, stripped look of a track frame. Hell, when I was pure bmx and mtb, I thought road looking frames and thin tires were laughably nerdy and now my eyes fix onto any bike that goes past and glaze slightly, to the extent that my girl has to check occasionally that I'm not looking at women.

It's not a matter of forcing her into riding, despite my imprecise syntax, but merely to open her up to the possibility of cycling without fear of becoming a ghost bike marker. (Or lycra clad commuter).