Considering that this is a Mando forum I'm rather surprised that nobody has mentioned the Duchess of Mandalor from the Clone Wars animated series, Satine Cryze.
If your gf decides to go that route you might like to know that there's someone on the RPF who's currently working on her formal costume, she might be able to help your gf with it. http://www.therpf.com/showthread.php?t=79244
in this case i would definitely go for half human half ghost bounty hunter Aurra Sing also known as Nashtah :] dangerous one she is :] she work with Fett once to :]
IMO, fem-mandos are lame and slave leia is totally and completely overdone. It's lost all its appeal. I also wouldn't recommend non-movie Jedi because nobody recognizes them. Try to stick to some of the cooler and unique female characters that are recognizable.