Other mistake: In the scene where Gen. Jackson leaves the bedroom of his sleeping wife and child, you can see a modern light switch covered over by a piece of plastic and paint near the door frame.
Continuity mistake: When Lee and Longstreet are surveying the map of the area, the position of the compass changes without anyone touching it. (01:02:00)
Factual error: Throughout most of the movie, Lee and Jackson are riding the wrong horses. Traveller was a dapple grey horse with dark grey mane and tail, and Little Sorrel was a dark rust-colored horse with a white star on his face. In the movie, Lee is shown riding a white horse with white mane and tail. At the beginning of the movie, Jackson's horse is correctly depicted as a sorrel with a white star. Then Jackson's horse is switched to a red chestnut with white blaze and four white socks.
Factual error: In 1861, neither Stonewall Jackson nor Robert E. Lee had heavy beards. Lee grew his after his resignation, and Jackson grew his during his campaigns.
Factual error: Throughout the movie, you'll notice some soldiers who are slightly plump, and others that are just plain fat (such as the "Santa-sized" Confederate soldier receiving the rifle from what one would assume to be a gunsmith). Because of strenuous marching and poor supplies (especially in the case of the Confederate army), by the time the Battle of First Bull Run came around, it would be highly unlikely that any of the soldiers would be as fat as those in the movie.
Factual error: Near the beginning of the movie the VMI boys are surrounding a flagpole about to tear the flag off it. The flag is CGI to hide the modern American flag waving there. However, when they zoom in to crowd pulling it down, it is a modern 50 star American flag. It isn't even a brief glimpse. It is there for several seconds and clear as day-modern flag.
Continuity mistake: When Gen. Blair is telling Colonel Lee that he has been authorized by President Lincoln to give him the rank of general, Blair is seen sitting in his chair leaning forward to talk but when the camera angle changes he is now seen leaning back and to his right. (00:05:40)
Factual error: The Confederate camp before the July 1861 Battle of Bull Run has shelter tents (AKA pup tents). These tents were first used by the Union army in late spring 1862. Conversely, the Union Army of the Potomac at Chancellorsville in May of 1863 is using common tents - the kind replaced by the shelter tent a year earlier.
Revealing mistake: Towards the end of the movie, as Jackson's Corps is attacking the exposed Federal right flank during the Battle of Chancellorsville, when the Confederate forces begin overrunning the Federal encampment, they sweep past two artillery pieces. Notice the second gun - it has a blocked barrel (filled with concrete). Must have been a memorial piece that was on/near the Chancellorsville battlefield.
Revealing mistake: When Jackson and his entourage ride in front of a big house at what he is told is Chancellor's Crossing, there is smoke coming out of the chimneys, especially the one on the left. Jackson and Jim stay there for almost 19 seconds and the smoke never moves, neither rising or blowing to the side as real smoke would. Obviously the house and background are a painting. (01:50:52)
Revealing mistake: As Jackson and his men ride up to a big house which he is told is at Chancellor's Crossing, there is smoke coming from the chimneys, especially the one at the left. The scene goes on for over 15 seconds and the smoke never moves. Even on a bitter cold night the smoke would rise and move even if slowly. Obviously the big house is a background painting. (01:50:00)
Answer: Yes, she did exist. Through books.google.com, I found a book "Cemeteries of Caroline County, Virginia: Private Cemeteries" by Herbert Ridgeway Collins, that confirms Jane did live, that she and Jackson were close, and that he arranged for her burial after her death.