You didn't specify which Chopin work you were refering to in your question, so I have assumed you are asking about "The Story of an Hour," which seems to fit your query.
Irony plays an all important part in this excellent short story. The central irony is built around the way in which Mrs. Mallard's husband is reported dead, which obviously acts as a catalyst in how it makes Mrs. Mallard realise how she has been oppressed in her marriage and now she can be "free" in her widowhood, but then how this fact is revealed to have been a mistake at the end of the story as Mr. Mallard comes into the house just after Mrs. Mallard has reconciled herself to her husband's loss and has began to really look forward to her freedom:
There would be no one to live for her during those coming years; she would live for herself. There would be no powerful will bending hers in that blind persistence with which men and women believe they have a right to impose a private will upon a fellow-creature.
It is thus highly ironic that Mr. Mallard should re-appear after Mrs. Mallard has made this realisation. In addition, let us not forget the crushing irony of the ending. Having been told that Mrs. Mallard suffers from "heart trouble," the ending ironically shows how everyone attributed her death to "joy that kills" as the sight of her beloved husband filled her with so much happiness that her heart ceased to work. Of course, knowing her thoughts of liberty and freedom, the reader is able to understand that in fact, it was the thought of returning to the oppressed state of marriage that made her heart give out.
As to the credibility of such ironies, I don't think they are presented in a way that makes us doubt their credibility. Perhaps it is a bit too convenient that Mr. Mallard returns precisely at the moment when Mrs. Mallard is looking forward to her single life and after she has experienced her epiphany, but life is made up of such ironies.