Why does Ellen tell Jethro that she is not going to be good company after reading the letter from Tom in Chapter 4?

In the letter, Tom tells his family about the Union soldiers overtaking Fort Henry and the battle at Donelson. He adds that on the journey to Donelson, a lot of the soldiers tossed their heavy blankets aside in order to lighten their loads. Sadly, by the time they arrived at Donelson, the weather turned cold and many of the soldiers froze to death in the snow. He concludes his letter by saying: "bein a soljer aint so much," leaving Ellen to worry.