In the story "Winter Dreams," Irene is a minor character; you might even say that her existence is more of a plot device than anything else. We know that she was engaged to Dexter briefly, before he slipped back into his obsession with pursuing Judy. But what do we really know about Irene besides this role that she plays in the plot?
Irene was light-haired and sweet and honorable, and a little stout, and she had two suitors whom she pleasantly relinquished when Dexter formally asked her to marry him.
So as the narrator tells us, Irene has a good moral character, is kind, and is perhaps not unattractive but a little on the heavy side. I mention that because it contrasts so starkly with Judy's character; we're told over and over about Judy's startling beauty. Here's something else we know, but it's not much:
[Dexter] stayed late at the dance. He sat for an hour with Irene Scheerer and talked about books and about music. He knew very little about either.
Apparently, then, Irene is probably a good conversationalist and knowledgeable about literature and music. The narration tells us that Dexter and Irene are engaged a few months later, but there's certainly no description of a romance between them that would even slightly compare to Dexter's romance with Judy in terms of passion and excitement.
Here's one more definite thing we're told about Irene:
It gave him a sense of solidity to go with her [to the dance at the University Club]--she was so sturdily popular, so intensely "great."
Those details make Irene seem a bit more interesting than before. Readers at this point may wonder if it's Dexter's indifference to Irene that makes her seem dull; perhaps her personality really is just as sparkling as Judy's, but it's unappreciated by Dexter.
Finally, the story is distinctly lacking in detail about what happens to Irene after Dexter abruptly breaks off their engagement in order to chase Judy some more. We could infer that Irene took the news well, without making a scene or seeking revenge on either Dexter or Judy, evincing again her own good social skills and classy personality.