How do I convince my girl to start riding?

Get her a bike as a gift instead of something she actually wants and you're a selfish asshole.
Get her a bike as an honest plea to get her to give it a try and at least it's honest.

This was part of my original point; if I buy her a bike will she see it as me trying to force her into riding, or would it be a welcome token of a desire to share one of my favourite things in life with someone I care about.

So far the only noises she had made against cycling are loosely based on safety, although now that someone has made a point about commuting in relation to female attire, I suspect that another strong issue may be not wanting to ruin the hour worth of meticulous preparation in her appearance before she leaves the house each day.