That's a good question actually! To be honest, it's very hard, even for me, to find or to make other girls interested in Bitcoin. Giving out these cute t-shirts was probably the closest I got to getting girl's interest.
http:// https://scontent-hkg3-1.xx.fbcdn.net/hphotos-frc3/t31.0-8/1965524_657331941022133_6146642929014352556_o.jpg

Another thing that might work is to explain the reason why the current financial system is so evil and problematic and why bitcoin is a solution to that. Nothing's more exciting than a REVOLUTION to make the world a better place If it's hard to explain or she's too impatient to listen, watch some documantaries like 'all wars are Bankers wars' or the 2nd part of Zeitgeist of 'The Lie we Live'.

Good luck!

P.S a short explanation I usually use goes something like this:
There are of course many problems in the world, but to make the biggest impact and positive change we need to address the source. Zoom out and you will see almost any issue can be linked back to the financial system. It’s not hard to understand. Some have the power to create money, others give up their time and energy to work for it. The ones who supply the money, control and rule this planet. As long as you accept their paper currency, you keep giving them this power. Wherever money goes, energy flows. Stop accepting their money and they'll soon lose their power. Use and store your value in a currency that cannot be controlled or manipulated, because it's transparent, decentralized and limited in supply. BITCOIN!