......Wow. I don't know whether to be sick from Mingyue's sheer scumminess or to shake her hand for being able to act so audaciously and scapegoat her own mother. Not to mention being willing to poison her own grandmother, who treated her so well, she might be an actual psychopath.
...Well, now she doesn't have anyone on her side. No grandmother, no mother, and no servant.
I'm pretty sure the laws of filial piety would apply every punishment attributed to poisoning your mother-in-law at least as much to condemning your birth mother to death.
Reminds me of that one Chinese Empress who started as a concubine. She smothered her own baby to pin the crime on the current empress.
I feel bad for concubine-mom, actually. She just wanted the best with her daughter and happened to get along with her mother in law. Rather, isn't the father kind of a weak-willed dumbass here? Does he have no capacity to investigate and judge on his own? Especially for his own wife and mother's sake.