Now, Thailand’s aristocracy has been thrown into fresh uproar after Vajiralongkorn decided he wants to promote Koi to the rank of queen. This news has been circulating for several weeks in royal circles, and it provoked intense opposition among leading members of branches of the extended Chakri dynasty such as the Yugala and Rangsit clans. Vajiralongkorn’s sister Princess Sirindhorn was also deeply unhappy about the news, because if Koi is elevated her own status in the royal hierarchy will move down another notch. Although Sirindhorn and senior aristocrats in the other branches of the royal family mostly gave up trying to influence the king long ago, and avoid disagreeing with him for their own safety, they felt so strongly about his latest plan that Sirindhorn went to see her brother to try to change his mind. This led to the most explosive development in the whole saga.

Two weeks ago, the palace announced that Sirindhorn had injured both of her ankles in a fall, and had been taken to hospital. As usual with royal health bulletins, it greatly understated the seriousness of her injuries, and of course it also failed to explain what had actually happened. According to well-placed sources, a furious row erupted during Sirindhorn’s meeting with her brother. She was knocked over by one of Vajiralongkorn’s dogs, and while she was lying on the ground he either stamped on her ankles or struck them with a cane, shattering both of them.

https://secretsiam.news/p/thailand-is-plunged-back-into-lse

I think she's more popular than her king brother.