to motivate a woman to use bitcoin i think it's very difficult.
logically, you can motivate by telling that the bitcoin can buy beauty

Just lure them into foodies and explain them how they can be used to buy pizzas and I think she will get convinced easily.

Moreover she might get insecure during the initial steps of trying the new payment system.
But dont make her worry any further.
Also if you get a chance where your nearby coffee shop accepts bitcoin then you try paying through bitcoins in front of her one day and she will obviously get curious the next second.
Funny that you mention this, since I've been taking my girlfriend to places where they accept bitcoin and I'm kinda showing off paying with my cell phone, in a very nerdy way albeit