Well, that's the downside to mail-order boots. Usually that process works fine, but sometimes it can be a challenge. It doesn't help either that every maker uses a slightly different "last," the mold on which the boot or shoe is built. Making lasts is part science, part art, and multiple variations therein. Some makers use lasts as much as a full size "off" straight sizing. Then, of course, there are substantial variations in the volume of different bootsthat is, the interior shape of the boot.
Your feet are very narrow, so when you buy boots that fit lengthwise, they're still too wide, right? For starters, what you could do is get a better picture of your precise foot size and shape. Do you buy shoes locally in your town? Can someone there spend a few minutes with you and carefully measure your feet with a Brannock device, the thing that measures foot length and width? Even then, I'd start by ordering boots a full size above what the Brannock device shows you need.
I'd also take care to ensure the shoes are made on a woman's last. Lots of women's hiking and climbing boots are simply men's shoes downsized a little. The Lady Makalu ($245; www.sportiva.com) is one such boot, so in theory it should be a good choice for you. La Sportiva's Glacier, a great all-around boot ($225), is built on a men's last. By all means, call the manufacturer (in La Sportiva's case, 303-443-8710) and talk your problem over. Try the Montrail Moraine ($235) as well; it is built on a woman's last, plus Montrail is known for making boots that fit a very wide cross-section of the boot-wearing population.