Along the theme of scary Chinese Empress Dowagers, Lu Zhi (wife of the founder of the Han Dynasty). I'll just quote
Wikipedia on how she dealt with one of her rivals:
" she had Qi's limbs chopped off, eyes gouged out, ears sliced off, forced her to drink a potion that made her mute, and thrown into a latrine."
Note that this is well after Concubine Qi was no longer any threat, but rather as revenge for a previous dispute.
She effectively ruled through a series of puppet emperors, and had her opponents murdered.