Fall, Winter, Early Spring Hiking Boots for Women

You may already know this, but a number of boots on http://www.rei.com/category/4500006_Women%27s+Footwear/q/Women%27s+Bootshave customer reviews that comment extensively on idiosyncrasies of size, width, etc. (Don't forget to ask your wife if her feet run wide or narrow!) I've usually managed to get within .5 of the correct size by reading reviews, and REI has a great return policy, so you could buy the two closest sizes and return whichever one doesn't fit when you get there.

Seconding Sorels; I got a brand-new pair on eBay for significantly less than retail.

I did winter hiking in Sorels for years, even managed to strap crampons on them for above treeline climbing. I've since moved on to plastic boots for higher stuff but I pull out the Sorels for snowshoeing and other hikes below treeline. They're also great to have for shoveling snow or walking to the train in a blizzard. Be sure to size them a bit larger since she'll be wearing heavy socks.

http://www.rei.com/product/772566 Keen Targhees are my new favorites this year, and are the only hiking boots I have ever had that don't give my delicate snowflake feet blisters after a day or two. They run a little big and have lots of room in the toebox, and I haven't had a problem getting fairly thick socks comfortably in them for days hiking on top of snowpack in the early spring in Denali. I feel like those, paired with warm socks and possibly a pair of these http://www.rei.com/product/778050 in situations of particular desparation keep me a lot happier than a pair of big clunky boots unless it is below the temperatures you mention, and I've done a significant amount of fall/winter hiking. I still go with the Sorrel-type boot for snowshoeing, though, just because they fit the bindings a lot better. Your wife's mileage may vary, however.

sorels for the win