My niece needs a bag for camping for college geology class trips. She is going to Wisconsin in March and South Dakota/Yellowstone in May. She thinks a 20 degree bag would be about right. This is not for backpacking, so weight and size are not really a concern. I bought the REI Lyra, but it is too snug on her. She probably needs a bag with a girth of 65 inches or more, and she is 5'5.5" tall.

Any recommendations? Most of the women's bags look too narrow. Most of the "20 degree" bags I've seen do not look like they have near enough loft to be warm at that temperature. She also told me that she can't sleep when she's hot, so I don't want to go too low with the temperature rating either. Price was somewhat of a consideration, but at this point I need to spend enough to get something that will work.

Mountain hardware ultra lamina is a good mid priced sleeping bag that could be used for all kinds of camping, car, backpacking.... Pretty roomy and warm to the specified temps.
http://www.mountainhardwear.com/ultralamina-15-regular-OU8490.html

The North Face Goliath is a wide bag, but I don't know that it comes in anything other than a zero degree rating. Kifaru makes a variety of bags with width and length options although I've never actually seen one. It's one of my wish-for items.

But if there is no backpacking and size and overheating are issues, I would suggest going to a department store and getting two inexpensive rectangular sleeping bags. This will allow either one or two bags to be used depending on temperature, will be wider, and probably even less expensive. One can be zipped up and the other used as a quilt over top that is easily removed if it gets too hot. The only real downside might be bulk and weight.

You could get something in a rectangular cut. Have her unzip the top part and use it as a quilt (zipper down). Need more cooling keep unzipping. Maybe this?: http://www.rei.com/product/846256/rei-siesta-25-sleeping-bag ... though its only rated to 25°F

Sounds an awful lot like a quilt.... you could get her a quilt! Enlightened Equipment has a 20°F rated short-wide prodigy-X quilt for $185: http://www.enlightenedequipment.com/?product=prodigyx-20-2

Big Agnes' Hog Park bag is a pretty wide and long synthetic. I think it's rated down to 20 degrees. I used to own one and had a ton of room to move around. I'm not sure if it would be too wide for a female, but it's not terribly expensive and is a pretty solid bag.

Thanks for all the suggestions. The MH Ultralamina didn't appear wide enough according to the published dimensions. Most of the Big Agnes bags don't have any fill on the bottom, and I wasn't sure that would work for her.

I tried Bass Pro and Cabela's. All the bags at Bass Pro looked about 9 feet long. I did find a "0 degree" bag at Cabela's that I thought would work, but the one I bought never fluffed up nearly as much as the one hanging in the store after 2 weeks, so I returned it.

I finally went with the Marmot Rockaway 0. She hasn't been able to try it out yet, but I'm hoping it's wide enough. The tag says it is EN rated for 20F and it looks lofty enough to actually be true.