The scene where she drinks is during the part with Yoojin (Yoona) returns to Korea after studying abroad at EsMod Fashion School in Paris after her father's death. Yoojin starts working in the markets of the Great East Gate, running her parent's clothing store but situation turns bad when she is confronted with debts and eviction of the store. She sets up a street vendor with Oh Daesan (Kwon Sangwoo) and is crying and complaining to him about her situation. This scene can be seen on Episode 2 will air on the 16th.
The rumor states that Yoona voluntarily drank to fully bring out her emotions and mood required for the filming.
The staff who were present at the filming site complimented Yoona upon her strong will. After Yoona finished filming for that scene she said she doesn't understand why guys would drink this bitter Soju(alcohol), shaking her head in puzzlement.
"Cinderella Man" a story of the Prince and Pauper will air beginning at 9:55 on the 15th.