Women’s sized synthetic jacket

Montbell does make a womens version of this jacket.

The women's Thermawrap is not hooded. However, I see that Montbell makes a women's Flatiron Parka. That might work.

Montbell has some fit issues sometimes (example – Thermawrap Vest, which they told me they were redesigning because of widespread fit issues), but they make great stuff. Try the Montbell women's Thermawrap Parka, which is hooded and very warm and will definitely work well if you use it as a belay jacket (over shell and all). My wife is a slender size 8 and 5 ft 6 and wears a Medium; I'm 6 ft 190 lbs slim athletic build and wear an XL – big enough to wear as a belay jacket at stops or in camp and fine on its own. Warmest synthetic jacket for the weight I've ever owned. The hood really adds to the warmth and you'll be glad you have it when you need it.

Sorry, I had the product name wrong on the 1st posting. It was the parka that she tried, and the unisex size didn't fit. I'm thinking now that we will have to drop the hood requirement to get something that fits, but is still lightweight and synthetic. So then we will be looking for a lightweight synthetic head – neck covering.

are you sizing against base layer or as a belay jacket?
as a belay jacket, go one size up and you should be fine.

Here's another two options-

Patagonia Micropuff- I own the men's version of the Micropuff pullover and it's sized large, for layering. It's almost too big. The women's full zip jacket is 14 ounces, and Paty's quality is second to none. It's also made 'earth friendly' with recycled materials.

Mountain Hardwear Compressor PL- Neither of us own this jacket, but we both tried it on. Frankly, I was surprised. Its a very well thought out jacket, with a lot of features, for a jacket so light. Mountain Hardwear makes good quality prodcut as well, and the weight isn't too bad at 12 ounces. My wife liked the fit and she's picky when it comes to this. I'd estimate it would fit most women just fine.

In my estimation, I'd place both the Patagonia Micropuff and the Compressor above the Montbell synthetic jackets in terms of warmth. If your wife is anything like mine, this is likely a good thing. She'll trade a few ounces for added warmth. Neither have a hood so you'll have to sort that out.

Patagonia does make a hooded Micro Puff parka for women, but they don't list it on their site anymore (new spring product line is up and the winter stuff is gone). You can find it at other retailers.

I'm quite happy with my men's Micro Puff. It's definitely sized to go over layers.

My wife has the Patagonia Micropuff and loves it.

Me too, and it is true to size. I got mine cheap last summer online somewhere out of Idaho. eBay tends to sell them as well.