I rarely read this forum, but I saw the thread title and had to have a look.
I have a helicopter CPL and FI rating; I also have a PPL(A). At the moment I work as a helicopter instructor. I'm also female.
To answer your questions, I'll start with the simplest ones first.
Women make up a very small percentage of commercial pilots of any type - 2-3% - and I think the percentage is about the same for rotary and fixed wing. However, since there are less helicopter pilots altogether, there are less women flying rotary aircraft. But does it matter? You won't get any prejudice, or little, once you reach commercial levels. Most of what you do get comes from the general public. And as for being rare, and the only woman in the flying school, CPL class, etc etc...you get used to it.
Everyone, but everyone, thinks helicopters are more fun to fly if they like hands-on flying. They're flexible, versatile, can land almost anywhere...there's nothing not to like.
There is no real point in learning to fly light aircraft first, as the two are very different. If you want to fly helicopters, learn to fly helicopters. Flying both is a lot of fun, but if I hadn't got my PPL(A) first I probably wouldn't have bothered - as it is I do the minimum number of hours to hang on to it.
When it comes to careers, this is more complicated. There is no rotary equivalent of the airlines, and few secure jobs in the rotary world. Basically, you need to get a CPL(H), and then something else, in order to be employable. Many people get an instructors rating, but while helicopter instructors are far better paid than their fixed swing counterparts, it's quite hard to make a living as an instructor unless you have something to fall back on in winter and bad weather. If you want to go for turbine flying, the North Sea Oil Companies are how most people start, but they are now expecting peope to pay for their own IR, which is expensive. Of course, if your daughter joins the military, everything gets paid for, if she thinks the life would suit her. But there are few helicopter jobs with pay equivalent to top airline jobs.
There are a lot of issues here, but if you want more detail on all of this, go to Rotorheads and do a search, as the subject has been covered ad infinitum on there.