Bit of a broad question but you could always try LibTech or GNU. Look for magne-traction technology. I'll let someone else recommend a specific women's board in this department - I only know that magne-traction is the bees knees if you're looking for edge hold.
From a more personal standpoint I've always had great success with Rome. I ride the northeast and am accustomed to icy and hard packed crap. Not to mention Rome is based in VT, which makes me think they know how to design boards to handle icy northeast winters.
Effective edge is what you want for hardpack, this is why racers, alpine boarders, and carvers use a board shape with a MUCH longer effective edge than us. I know some guys love the mange-traction, frostbite edges, etc. but I have yet to see any racers win on boards with bumps in the edges.
So ultimately, if you want to stick with a traditional board, look for something with blunted tips.
My board is a 160 and has over 140 cm of effective edge, while most 160 cm boards have somewhere from 120-125 cm effective edge.
Rossignol Diva, Rossignol Frenemy, Roxy Eminence, GNU B-Pro, Smokin Vixen
Those are just some boards with magnetraction...
Then maybe Arbor Push or Arbor Cadence.
Dont discount the Poparrazi in the arbor line. Also with grip tech. Just from reading about it people seem to consider its hold quite good on the hard stuff. Thinking about this one for my wife actually.
Thats a race board which isbasically effective edge and nothing else. The nose is probably 50mm and the tail 20mm so yes they are VERY blunt.
What poutanen is getting at is dont look at total board length as this the sum of the effective edge,nose and tail length. Look at effective edge length and go for a big one, then to try and keep the overall board length down something a with blunt (short) nose and tail length.