Tsu is right that there are a bunch of factors to consider here.
The first, and the worst one for your story, is the state this is located in. Maryland has about 600 brush fires per year. Average size? About six to eight acres. See
http://dnr.maryland.gov/forests/wfm.asp. Needless to say, most brush fires are very small. A large brush fire in Maryland might have a hundred acres, which is less than a sixth of a square mile.
Out west and in Florida they measure large fires in square miles. A big brush fire in the Northeast just isn't.
The Northeast doesn't have crown fires very frequently. Because of population density and fire towers, brush fires just don't get a chance to get going. Crown fires require some heat before they get going. These are the big fires out west. California and Florida have brush-type fires.
The Northeast have low level brush fires where most of the fuel is pine needles and leaves on the forest floor. Most living trees and brush in the Northeast have a high water content and don't tend to burn. We also have grass fires, which do burn a bit hotter as the fuel load is higher in height.
Frequently in brush fires you can literally walk right over the fire. However, let's give you the formula for a big, Northeast fire.
First off, you start off with a Red Flag day. This is a day with extremely low humidity and high winds (25 mph+). The forest consists of a lot of dead and fallen trees, approximately ten years old. Terrain is uphill.
Fire will spread faster than you can walk, as long as the wind blows. Flame height might hit 5 to 10 feet. As soon as the wind stops blowing, flames would come down to the 3 - 5 foot range. And as soon as it tops the ridge, it will die back down.
Main difficulty fighting it will be getting personal and equipment to the scene. Normally it would be contained within about a quarter of a mile of when the fire department arrives. If the terrain is really bad, it might take until the next day.
Worst brush fire I went to wasn't contained until the next day. Burned about 800 acres. The terrain was so bad that the deer had different size legs so that they could stand level. It took another two days after it was contained to put the whole thing out. For people who've been on fire lines out west, it was very boring.
Now looking at your specific facts:
I'm sorry but I think your editor is right that you have a problem. I'd contact the Maryland Department of Natural Resources for more information and ideas on how to make your story work.
Best of luck,
Jim Clark-Dawe
Former volunteer firefighter/EMT