She does indeed counteract her husband's callousness here, acting as buffer to Mr. Twist's icy contempt.
I've discussed this elsewhere, but I am always amazed that, though Mr. Twist does show icy contempt, it does not seem to be a reaction to Ennis and Jack's gayness. Rather, he's mad at Ennis for letting Jack down, and/or Jack for not following through on his plan to help out at the ranch. I think this is intended to show Ennis discovering that not everyone reacts as negatively to homosexuality as he assumes they do.
Ennis: “You ever get the feelin’...I don’t know...when you’re in town and someone looks at you, suspicious, like he knows?”
I wonder whether there was a specific incident to make Ennis feel that way. It wouldn’t have to be something that happened to him--maybe he saw someone else being harassed. That’d be enough to trigger his startle point.
I always think of it as a reaction to Alma's Thanksgiving confrontation. He figures if she knows, lots of people must know, either because she let the secret out (if only to her husband, but he's the town grocer), or because they figured it out the same way she did (since he doesn't know what she saw in the stairwell).