The allergens produced by female cats are often less potent than that of male cats, which is probably why people mildly allergic to cats sometimes (but not always) react less, or not at all to female cats. Thats not to say that if you don't react to most female cats, that any female cat will be okay, regardless if they've ever been around a male or not. Individual cats will vary.
For instance, I've lived with both male and female cats. I am less allergic to my female cats than I was to my roommate's male cats. Though I am less allergic to my cats, they still occasionally cause me to have an allergic reaction. But between my 2 female cats, I am more allergic to Sadie than I am to Trixie.
How allergy-causing a cat is will depend on many things. Some of these things can be controlled. Cats who shed a lot will leave more dander laying around the home. Feeding a high quality diet will help to improve skin and coat health which will reduce shedding. Brushing the cat (by a non-allergic person) will also help to control the amount of hair (and therefor dander) around the home.
Frequent vaccuuming and dusting is important (but can stir up allergens so is best done by a non-allergic person). Investing in a good HEPA air purifier will help to remove airborn allergens.
Giving the cat a bath on a regular basis (every 1-2 weeks) will significantly help. The cat needs to have her fur completely wet, though, to remove most of the dander.
The allergic person can also take daily allergy medication if needed. I use walgreens generic brand of claritin, and when I buy it on sale, it costs me about 20 cents per day.
I think taking the right steps to prevent allergies is better than relying on a paticular breed, but as far as hypo-allergenic breeds go, the only breed I've heard of that might be non-allergienic is the Siberian. The hairless or very short haired breeds seem to affect some people less, as well, since the shedding factor is reduced.