We don't get to know Mrs. Dexter very much outside of what Jamie tells us about her. Think about it this way: How much do you tell your friends about mommy dearest? Some, but probably not a whole lot when it comes to her complexities. From Jamie, we know her mom cares a lot about her kids. She might keep a lid on her emotions, but they spill out when TJ goes off to war. Can you blame her?
We can't. Jamie, on the other hand, doesn't get it—she's never seen her mom act this way. To Jamie, there's no crying in war. Listen to what she tells us about how her mom handles it:
My mother, who, despite a certain talent for keeping a stuff upper lip during trying times, kept having minor emotional outbursts, like when she was doing dishes by herself in the kitchen and suddenly cried out to no one, "Whose idea was it to have this war, anyway?" (8.1)
It's a big change, for sure.
This tells us that Mrs. Dexter is usually calm, composed, and has everything together. Another way of putting it? She's your typical army mom: She knows war is a part of the gig and learns how to deal with it.