Sienna was the former High Leader of the White Fang. According to The World of RWBY: The Official Companion book, Sienna's first action as high leader of the White Fang was to use Violence and fear against humanity. During her time as leader, it was shown and implied that all of members of the White Fang greatly respected and believed in her usage of violence to demand respect from Humanity. However, there were some who took her beliefs too far, and saw her as too soft, such as Adam Taurus and the Albain brothers. As such, Adam was able to convince a number of White Fang members including her royal guards to attempt a coup to overthrow her.
Back when the White Fang was led by Ghira Belladonna, Sienna and Adam understood one another, shown when she nodded for him to engage the humans attacking their convoy and later called him a hero after he killed a human to save Ghira's life. Later when they both attacked a Schnee Dust Company facility, she and Adam both used brutal attacks against the human security guards. She did however stop him from killing one of the guards to focus on the mission, not actually caring about the guard. She openly supported Adam's methods and gave him control of the Vale branch of the White Fang while stating if he continued on his current path that he would eventually work by her side.
In "Dread in the Air", their relationship was shown to be strained as Sienna criticized his involvement in the Fall of Beacon, citing how it actually hurt the White Fang in the long run. Once she realized Adam was trying to overthrow her, she defiantly proclaimed she would never serve him, right before Adam took her life and her position as High Leader.
Not much interaction was shown between them, but during the convoy attack, it was shown that their different opinions on conflict resolution and Adam killing a human hurt their working relationship and started to form a rift between them, resulting in Ghira stepping down as High Leader and Sienna taking his place.
Although their ideology and belief's clashed with each other, it was shown that Ghira still harbored strong respect for Sienna and what she stood for and while not advocating her usage of fear, terrorism and violence against Humanity to gain their rightfully deserved respect, Ghira did agree with her that the Faunus people deserved better than what they have and that they should be seen and treated as equals by humanity.