Observant/Cautious/Perceptive Female Lead (like Sword and Brocade)?

I never start currently-airing dramas for fear of getting addicted and having to wait for new episodes but started Sword and Brocade on a whim because nothing else seemed appealing and now...my fear has come true! This is a masterpiece of a drama but that main thing that keeps my attention is the female lead. I was initially turned off by the "extremely assertive" description in the summary but I was pleased to note that while she may think that way, she's more low-key on the outside. I really like the way she is observant and perceptive and how she always maintains her composure - she reminds me a lot of Minglan. Characteristics I am looking for:

• Knows how to hold her temper or fake her emotions
• Observant of the people or situation around her
• Thinks (a lot) before she acts. Or, chooses not to act. It may look like she is being a doormat but knows when to pick her battles. 
• Similarly, generally lays low and/or knows when to let sleeping dogs lie 

Another example is Hong Seol is Cheese in the Trap. Any country/time period/age group is fine but must be good acting - these characters emote a lot with their eyes/facial expression/body language and if the actress cannot properly express it, the entire character falls flat. 

Thank you very much!

The Story of Ming Lan is basically what your looking for! It is a slow burn in terms of romance and general setup but it’s well worth it!

I haven't watched that series yet, but based off your character description, I'd say Story of Yanxi Palace fits perfectly!

Thank you everyone for your suggestions. I will add Renascence and Flower of Evil to list!! 

I alluded to Minglan in the Story of Minglan but didn't make it obvious, oops. She's my #1 for this type of character. Part of the reason why she is so smart is cause she knows how to be patient and put on a smiling front. When she does act though, it's a killing blow. She fits the phrase "jūnzǐ bàochóu, shí nián wèi wǎn /when a nobleman takes revenge, ten years is not too late" so well. I think the reason why I enjoy this character so much is that it is so applicable to real life - sometimes you have to put your emotions aside and just 'grin and bear it'. 

Story of Yanxi Palace is on my watchlist (at some point) but, from what I've heard, I don't think it applies here. While the FL is very smart, she's not cautious at all. She's more...plucky and headstrong and gives off the "don't mess with me" vibes." Which is fine but realistically, given the position she was in, she would not have been able to get away with that and it ruins believability. Like, irl, you cannot tell your supervisor to screw off and not expect to get fired. While Minglan and Shiyi may do a couple of unrealistic things, the show has them succeed by having them still follow the rules of the time and their position. Then again, this is all from what I've heard so maybe I just need to watch it and form my own opinion.