Every ISTP I can think of is male... and the personality type tends to skew more towards classic male stereotypes. I know I have met female ISTP's, but I wouldn't be able to pick them out in a crowd.
How to female ISTP's behave?
**My best guess would be that they would tend to play down their true character due to the stereotypical male characteristics. If they don't, they would come off to be somewhat tomboyish.
Also, I'd guess you'd find them playing sports and interested in more technical areas like practical science and computers. What do you guys think? Any good female ISTP descriptions, or dead giveaways that have influenced you to believe the girl is an ISTP?