My wife is a foot shorter and eighty pounds lighter than me, and we find the cold affects her a lot more. She carries a 20 degree bag year round along with down booties, down vest, synthetic hooded jacket, and warm gloves. One thing to consider is if your significant other is less experienced than you, you may be paying better attention to nutrition and exertion levels than them, and are likely more conditioned. The exhaustion, along with doing the bulk of the camp chores while they assist or simply watch, can lead to wildly different perspectives on the weather. It my be different mentally, as well; I am okay with discomfort but the wife is not.
I guess what I'm saying is women's insulation needs are likely associated more with experience than anything else.