I considered this question, at least in relation to Wu and Lü, in an essay I wrote for the Smithsonian a few years ago. While it addresses only a part of your query – covering some of the key reasons why powerful women were demonised – you may like to read it while you wait for answers to the question of whether any powerful women have been considered 'virtuous', so I am pasting the text of the essay below.

Most nations of note have had at least one great female leader. Not the United States, of course, but one thinks readily enough of Hatshepsut of ancient Egypt, Russia’s astonishing Catherine the Great, or Trung Trac of Vietnam.

These women were rarely chosen by their people. They came to power, mostly, by default or stealth; a king had no sons, or an intelligent queen usurped the powers of her useless husband. However they rose, though, it has always been harder for a woman to rule effectively than it was for a man–more so in the earlier periods of history, when monarchs were first and foremost military leaders, and power was often seized by force.

So queens and empresses regnant were forced to rule like men, and yet roundly criticized when they did so. Sweden’s fascinating Queen Christina was nearly as infamous for eschewing her sidesaddle and riding in breeches as she was for the more momentous decision that she took to convert to Catholicism–while, mustering her troops in 1588 as the Spanish Armada sailed up the Channel, even Elizabeth I felt constrained to begin a morale-boosting address with a denial of her sex: “I know I have the body of a weak and feeble woman, but I have the heart and stomach of a king, and a king of England too.”

Of all these female rulers, though, none has aroused so much controversy, or wielded such great power, as a monarch whose real achievements and character remain obscured behind layers of obloquy. Her name was Wu Zetian, and in the seventh century A.D. she became the only woman in more than 3,000 years of Chinese history to rule in her own right.

Wu (she is always known by her surname) has every claim to be considered a great empress. She held power, in one guise or another, for more than half a century, first as consort of the ineffectual Gaozong Emperor, then as the power behind the throne held by her youngest son, and finally (from 690 until shortly before her death in 705) as monarch. Ruthless and decisive, she stabilized and consolidated the Tang dynasty at a time when it appeared to be crumbling–a significant achievement, since the Tang period is reckoned the golden age of Chinese civilization. T.H. Barrett’s recent book even suggests (on no firm evidence) that the empress was the most important early promoter of printing in the world.

Yet Wu has had a pretty bad press. For centuries she was excoriated by Chinese historians as an offender against a way of life. She was painted as a usurper who was both physically cruel and erotically wanton; she first came to prominence, it was hinted, because she was willing to gratify certain of the Taizong emperor‘s more unusual sexual appetites. “With a heart like a serpent and a nature like that of a wolf,” one contemporary summed up, “she favored evil sycophants and destroyed good and loyal officials.” A small sampling of the empress’s other crimes followed: “She killed her sister, butchered her elder brothers, murdered the ruler, poisoned her mother. She is hated by gods and men alike.”

Just how accurate this picture of Wu is remains a matter of debate. One reason, as we have already had cause to note in this blog, is the official nature and lack of diversity among the sources that survive for early Chinese history; another is that imperial history was written to provide lessons for future rulers, and as such tended to be weighted heavily against usurpers (which Wu was) and anyone who offended the Confucian sensibilities of the scholars who labored over them (which Wu did simply by being a woman). A third problem is that the empress, who was well aware of both these biases, was not averse to tampering with the record herself; a fourth is that some other accounts of her reign were written by relatives who had good cause to loathe her. It is a challenge to recover real people from this morass of bias.

The most serious charges against Wu are handily summarized in Mary Anderson’s collection of imperial scuttlebutt, Hidden Power, which reports that she “wiped out twelve collateral branches of the Tang clan” and had the heads of two rebellious princes hacked off and brought to her in her palace. Among a raft of other allegations are the suggestions that she ordered the suicides of a grandson and granddaughter who had dared to criticize her and later poisoned her husband, who–very unusually for a Chinese emperor–died unobserved and alone, even though tradition held that the entire family should assemble around the imperial death bed to attest to any last words.

Even today, Wu remains infamous for the spectacularly ruthless way in which she supposedly disposed of Gaozong’s first wife, the empress Wang, and a senior and more favored consort known as the Pure Concubine. According to the histories of the period, Wu smothered her own week-old daughter by Gaozong and blamed the baby’s death on Wang, who was the last person to have held her. The emperor believed her story, and Wang was demoted and imprisoned in a distant part of the palace, soon to be joined by the Pure Concubine. Having risen to be empress in Wang’s stead, Wu ordered that both women’s hands and feet be lopped off and had their mutilated bodies tossed into a vat of wine, leaving them to drown with the comment: “Now these two witches can get drunk to their bones.”

As if infanticide, torture and murder were not scandalous enough, Wu was also believed to have ended her reign by enjoying a succession of erotic encounters which the historians of the day portrayed as all the more shocking for being the indulgences of a woman of advanced age. According to Anderson, servants

provided her with a string of virile lovers such as one lusty, big-limbed lout of a peddler, whom she allowed to frequent her private apartments…. In her seventies, Wu showered special favor on two smooth-cheeked brothers, the Zhang brothers, former boy singers, the nature of whose private relationship with their imperial mistress has never been precisely determined. One of the brothers, she declared, had “a face as beautiful as a lotus flower,” while it is said she valued the other for his talents in the bedchamber…. [By 705] the empress, greatly weakened by infirmity and old age, would allow no one but the Zhang brothers by her side.

Determining the truth about this welter of innuendo is all but impossible, and matters are complicated by the fact that little is known of Wu’s earliest years. She was the daughter of a minor general called Duke Ding of Ying, and came to the palace as a concubine in about 636–an honor that suggests that she was very beautiful, since, as Jonathan Clements remarks, “admission to the ranks of palace concubines was equivalent to winning a beauty contest of the most gorgeous women in the medieval world.” But mere beauty was not sufficient to elevate the poorly connected teenage Wu past the fifth rank of palace women, a menial position whose duties were those of a maid, not a temptress.