I compare the shooting hobby to my primary hobby, which is horses. From what I have seen of hobby riders, it's about 90% female, so the opposite of what we're talking about here. Maybe it's the case that, as a hobby, guns are more interesting to men like horses are more interesting to women (I realize I'm speaking in very broad generalities). At competitive levels that changes significantly, but at the hobby level it seems to hold.
I shoot weekly at an indoor range and the only other female who has ever been there at the same time is one of my good friends when we go together. I did see a dad with his son and daughter there once, and that brought a happy smile to my face (they were using these cute character paper plates from a birthday party as targets, I almost asked if I could have one).
I suspect the time demands of marriage and children (often in addition to work) affect the frequency with which female shooters get to the range. I'm the only one in my social circle who isn't married with a young child, so my time outside of work is my own. For my shooting friend, her husband either has to be available or she has to arrange for a sitter in order to go to the range with me (or do anything without her daughter). Maybe for her upcoming birthday I'll give her an afternoon of child watching so she and her husband can go shooting together.
I bet if range trips were more of a "family affair" this could change, but the demographics are working against you to get females in their late 20s-30s-early 40s. Kids, husband (or not), house, job, friends... Range time would be pretty far down on the list and may not be the top priority for whatever little "me time" there is. Luckily, my shooting friend works at the same company as me so she can combine range time with "friend time", and we can talk about work things, too. Always multi-tasking...