There was only one friend she knew of that was Ennis. Hence her comment, "where bluebird sing and a whiskey spring." it was related to Jack and Ennis. Ennis was the friend Jack talk about. The knowledge of the relationship between them, well, I think she did know, but quietly accepted it.
She did know that Ennis was only one closer to Jack than she was. The comment about Jack keeping all his friend numbers in his head, was more of stab at Ennis. But then she told him to contact Jack's parents about the disposition of his ashes, on Brokeback which she thought was pretend place, it wasn't. She knew Ennis was an important part of Jack's life. How hard it must have been for her to speak to her rival.
Lureen knew and excepted what was going on, Alma couldn't. She compensated for it, by being more involve with business, and dealing with the idea you're not what your husband wants.