I'd just note that sleeping bag temperature ratings aren't terribly consistent between manufacturers, and sometimes between bags from the same manufacturers. Some bags are rated to be comfortable at the rated temperature with minimal clothing, while (in my experience) most are rated for use with clothing to keep someone alive although not necessarily comfortable. You'll just have to try them out to see what feels right.
I find that women/girls typically don't take lower temperatures as well as men (ask my wife how I know). Therm-a-Rest sells their women's sleeping pad versions with more insulation overall, and even more in the torso and feet (areas where women are generally more sensitive to cold). They cut out "stars" in the men's versions evenly throughout the length, but do so less in the women's versions in certain areas.
When I went camping with my wife, she brought along a supposedly 30°F rated sleeping bag. Overnight temps were about 40°F, and she was miserable. I pulled out my backpacking sleeping bag I used earlier in the trip, and she used that inside her bag. Be sure to bring extra clothing layers. Some sort of long synthetic underwear can help. You might want to layer them as it might get colder between 1-5 AM, and might start warming up in early morning. Bring along some wool or synthetic beanie hats to wear while your family sleeps. Keeping your ears and head warm goes a long way towards comfort when it gets down into the 40's.
