Before I begin, let me say: I think Queen Dowager Cho is a great addition to the list of greatest villains in
Sageuks. The actress killed it in her role.

As I was watching this series, I kept thinking: "Queen Dowager is displaying symptoms of ASPD."
ASPD stands for Antisocial personality disorder. It's often characterized by impulsive, irresponsible and criminal  behaviour. Someone with ASPD is usually manipulative, deceitful and doesn't care about other 
people's feelings. A lot of villains could be diagnosed with ASPD.
So why did Queen Dowager stick out so much?

I kept thinking of all the symptoms she displays. According to the Diagnostic and Statistical Manual of Mental Disorders (edition 5) you need to meet 4 criterion in order to be diagnosed with ASPD.
Queen Dowager fits criterion A, exploits, manipulates or violates the rights of others which includes the following behaviours:
(1) failure to obey laws and norms by engaging in behavior which would warrant criminal arrest
(2) Lying, deceiving and manipulating
(3) Impulsive behaviour
(4) Blatantly disregards safety of others
(5) Lack of remorse for actions
 
One of her quotes really stood out to me in this regard:
"I am a winner.
They just paid the price for losing."
 


She also fits criterion B, as she is older than 18. We don't know, however, if she's been this way since before
she was 15. We also don't know for sure if her behaviour isn't due to schizophrenia or bipolar disorder.
It doesn't seem likely that she has those, but I could be wrong.

This might be a silly post, as it's impossible to diagnose a character with the limited information that we as
viewers get, but I just couldn't shake this thought and I guess I wanted to share it.

Disclaimer: clinical psychology isn't my field of expertise. I have studied psychology though. 
This is just my personal opinion.