You are right to indicate that in the early part of this story and the conversation that we are privy to between Jig and her American partner, she uses sarcasm. Consider the following example. When they receive their beers, and Jig complains that it tastes like licorice, her partner says that everything tastes like licorice. Note how Jig responds:
"Yes," said the girl. "Everything tastes of licorice. Especially all the things you've waited so long for, like absinthe."
In response to her partner telling her to stop this, she replies "I was being amused. I was having a fine time." This is of course one of the first indication that something is seriously wrong in this relationship, and that Jig is using sarcasm to express both her anger and also the intense distress that she feels in her situation. She clearly knows and understands that she faces a choice between aborting her baby and saving her relationship to this man, and keeping the baby but ending the relationship. The sarcasm is a natural response to the intense stress that she feels as a result of this situation.