That was The Chill Sisters, brooklyn. It's sometimes referred to by another name, something like The Amazing Golden Princesses (give or take) and it remains one of my favorites altho I've only seen 10 K-dramas to date. Mom's Dead Upset is a close second.
Boy, this is thread is really confusing me. Ban Hyueong was in As High As the Sky, right? I thought Grandma Curlers was the "step-mother" in As High as the Sky -- the one who eventually share a room with Ban Hyueong. And who is the male attorney's mother in MDU. Yun Yeojeong was in Pure In the Heart. N'est pas? Ki Taeyoung & Lee Sangwo look sooo much alike that even side by side, it's a bit hard to tell who is who.