This is a rather complex question for a typical encyclopedia, so I'm not too surprised that you couldn't find it on Wiki.

TLDR

• Wu Zetian becoming the de jure female ruler does not signify the society's acceptance of ALL female rulers. Her rise to power and eventually the throne was a complex mix of social and political issue, as well as her own capabilities .

All these intricacies are one-of-a-kind in history, and hardly reproducible, which is why Zetian's successor dilemma was never about her daughter because she knew herself that it's not likely for not another female ruler to rise anytime soon. In fact, this is probably why even though there were many female rulers throughout Chinese history, only Wu Zetian was recognized officially as the de jure ruler of China. One of her daughters Princess Taiping did tried to replicate her mother's success, but was unsuccessful. Again, another evidence for the fact that Zetian's journey is not really reproducible.

• For her successor, Zetian initially preferred her own family, the Wu family, which is represented by her nephew. But due to political complications and the final blow by one particularly interesting event, 营州之乱 (Conflicts at Yingzhou, somewhere near Liaoning today), she eventually decided to return power back to her son, i.e the Li family.

So now we start with the reason for her rise to power.

First, politics within the royal family. No one can mention successor politics in Tang dynasty without mentioning the Xuanwu Gate Incident . In essence, Emperor Taizong of Tang, then the 2nd son of the previous emperor, lead a palace coup for the throne of the Tang dynasty, killing his elder brother, the Crown Prince, and his younger bother who supported the crown prince. Now, Chinese empires traditionally has always been about setting up the eldest son of the official wife of the emperor/empress as the Crown Prince. This coup changed this fixation in the sense that hey look at Taizong, he did it! So why can't I? As a result of Taizong's success as well, the Tang successor system was a mess, there aren't any rules because Taizong's very existence is against normal rules. This is why Taizong had a bunch of successor issues of his own, but that's not within the scope here.

Fast forward to Emperor Gaozong of Tang, Taizong's son and Zetian's husband. At first, all was good. After Zetian became the empress and gave birth to her son, the Crown Prince title was given to their first son, Li Hong (李 弘). However, a few things then happened. First was that Zetian gave birth to more sons. Second was that Hong died soon after. Lastly, Gaozong got ill. The illness was called 风眩病, similar to modern day Cardiovascular diseases. This illness caused Gaozong to have frequent headaches, felt dizzy very frequently, greatly impairing his ability to rule. As a result, Zetian was able to gain power and say in the imperial court and decision-makings under the name of 'helping out' the sick emperor/husband. With the 'rightfully' eldest son dead and a bunch of other sons by Zetian alive, there were rising tensions between each prince for that title. Whilst the rising power of Zetian become conflicting with the powers of the princes and Crown Prince wannabes.

Gaozong was more trusting of Zetian (for reasons I will explain later on)and granted her more power as time goes on, and with the aforementioned chaotic successor system, there was no consensus on who should be the Crowned Princes and no system to ensure the power and influence of Crowned princes or even normal princes. This continued on even after Gaozong's death, providing a good 'reason' for and offered almost no resistance to Zetian's actions of exerting more dominance and power and eventually becoming the ultimate ruler. She then use her power and took opportunity of some events to kill off many Li family royal members and any officials/royalties that were against her rule, paving the way for a smooth transition which she was eventually able to accomplish.

Another reason was about Zetian herself. She was known to be capable and smart. She aided Gaozong tremendously in the management of different issues. She supported Gaozong in his various decisions , especially his struggle for power with influential officials from his father's era. In fact, she was so valuable and important as a sort of advisor and someone with common interests that Gaozong was willing to go against the general court opinion and establish Zetian as his official wife --- Zetian was from a poor family and the court officials were very against their divine emperor marrying a poor lowly girl. This trust is probably why Gaozong was willing to give her so much power when he was ill, even to the extent of expressing intent to pass the throne to her in

帝多疾，欲逊位 武后 《新唐书》

Emperor was severely ill, and wish to pass the throne to Empress Wu.

Last reason for her rise to power was support from the society. Not because she was woman but because of the groups she represented and helped. This has to do with some ancient influences since the Three Kingdoms, so do bear with me. Basically, since the Three Kingdoms era and Jin Dynasty period that followed, there was a rise in power of clans, often as rich and educated people with the same family name related by blood coming together for form a group with common interests. Because they were already somewhat influential and rich prior to the agglomeration, them coming together in a clan only further strengthened their influences and wealth. As a result, these clans were super powerful, so much that even nobilities of dynasties and kingdoms often have to arrange marriage with them to garner their support and make use of their influences. While it's all rosy within the clans, the commoners suffered. All the wealth and status were largely occupied by the clans, the divide was so huge that there was this saying of

上品 无寒门 , 下 品无势族 《晋书卷四十五刘毅传》

No one in the upper-class was of poor, commoner origins, and no one in the lower-class was from any clans.

Tang Dynasty, since Taizong's time, has largely adopted policies to suppress the influences of these clans while trying to increase social mobility for the lower classes through measures like using more officials from lowly backgrounds, limiting inter-marriages between large clans etc. With the emperors before her setting the trend and paving the way, Wu Zetian, without much resistance, continued in this direction, she encouraged and improved the 科举 (Keju) , a proto-meritocratic system in China. She 'discovered' and promoted many capable officials from commoner backgrounds, and used them in key areas, such as the famous Di Renjie. With the array of things she did to neutralise this social divide and improve the status and influence of the lower class, she was pretty popular and well-liked amongst the general non-clan affiliated populations. Those people and the officials representing them were the key driver and members Zetian used to crush any opposition to her power and eventual rule. They were also the main people that were fine and not against her becoming an emperor, because they wanted more of her policies that bring wealth and influence to the traditionally poor and deprived lower classes.

With these 3 reasons , we can see that it's a very unique combination of events that are not really reproducible. Tang's chaotic and weak successor system is pretty much uniquely Tang because of the coup. Not all woman are capable of managing an empire like her. And the social situation of her time was also unique, she was able to follow the footsteps of her predecessors and garner support of the commoners--- the clans, following Tang's reforming policies and political conflict after Tang's fall a few hundred years later, disappeared from history by the 10th century.