I really like Joo-wol as a side character. She's very good at her job, she's quite intelligent, and she is running a successful business. She doesn't just gossip aimlessly, she has a good idea of what is true and false and is often a step ahead of everyone else.
I also love that she's such good friends with Mu-deok because they do suit each other. They both have pretty lax morals (Joo-wol instantly agrees to sell the spirit plaque illegally), mostly out for themselves but will protect people around them (Joo-wol shows concern for her staff, especially the guards), very intuitive (Joo-wol changes her reactions to customers rapidly and reads Mu-deok very well) and will flatter without shame.
I hope that Cho Yeong reestablishes her bestie relationship with Joo-wol because I love them together in S1.
Also, her outfits are awesome!