Why not?
My understanding is with the modern (shaped) skis, length = skier weight. The key is to size your ski by weight, not by height. Say, the manufacturer assumes a women of 5'8 weighing on average 150-180, then that's probably the length you should be getting instead of skis for 5'4 tall lady! (if I size my skis by height, I'd end up with skis too long due to my way below average weight)
Although just like I'm too light for the shortest of most men's ski, at 170# you might not find too many lady's ski long enough for your weight...
Well, first - I meant that I wouldn't necessarily go up in length from the length she's comfortable on, not from whatever the height chart may say. I guess I'm assuming she's already got an idea of what sort of length she feels comfortable on.
Because while weight is certainly a factor, I still think that height is a factor too. No matter how heavy or muscular you are, if you have short legs it's just going to be unwieldy and difficult to manage if you're on skis that are extra long. Maybe it wouldn't matter if you were just skiing big turns on groomers, but if you're trying to ski trees or hiking or God forbid, do a kick turn - the length of your legs compared to your skis does make a difference. I think that for many people, as your weight goes up, you prefer a stiffer ski, not necessarily a longer ski (though you might like a somewhat longer ski). Now that's where it gets weird though, because at that point you have to account for your skiing style on the finesse/power spectrum. I know some big guys - like 230+lbs who like skis like Pocket Rockets, which are very soft, and by all logic they should easily overpower, but they do great with them.
And then, I think you also have to determine the use for the skis in question too. I think in a person's quiver, there are places for various lengths of skis. I have everything from a 160 to a 185, and my choice for an "everyday" ski is around a 175-178. My powder skis are the longest for flotation. So what I meant by that comment was just that for a one ski quiver, I'd stick with the length you know you're comfortable on, and only go longer if they were for powder skis or some such thing.
Of course, the easiest way to solve it is for her to demo. I agree that most women's skis are probably not what she is looking for (I know they aren't for me), but I think something reasonably stiff like the Volkl Aura would likely work for her. Of course, there are plenty of unisex skis that would be excellent options as well.
(And I also think it works in reverse - if you had an extremely tall, but lightweight person, I think if you go too short, you're going to create fore/aft balance issues. Instead, I'd recommend something at least close to a "normal" length for their height, but a softer flexing ski that they will be able to flex with their weight. If you went too short to compensate for the weight, you'd be effectively putting them on ski-blades. Which might be a nice training tool, but wouldn't be what they want for normal skiing. Just my 2 cents.)