So it is definitely going to drive me nuts if I can't remember what drama this was, and looking through my list, nothing is popping out.
The only scene that is standing out to me is where the female lead's mother comes back and acts like she is well off. However, she is only there to get money from the daughter, and I think the male lead finds this out. Then the revelation happens that the mother wasn't getting the money for herself, but for another daughter she has who is extremely ill. The female lead realizes she has a younger sister and meets the mother and the sister as they leave at the airport.
Save me~