Warning: SPOILERS ahead for His Dark Materials season 2, episode 2, "The Cave".
His Dark Materials season 2 has seen the war between the Magisterium and the witches intensify - but there are signs that Mrs. Coulter herself might be harboring a secret witch heritage. Based on the novels by Philip Pullman, His Dark Materials was a joint effort between the BBC and HBO. Centered on Lyra Belacqua (Dafne Keen) and Will Parry (Amir Wilson), the first season saw them embark on separate journeys that would ultimately take them into parallel universes. His Dark Materials season 2 saw them finally come together in order to solve the mysteries surrounding Dust, Will's connection to a mysterious knife, and members of their respective families.
For Lyra, those members are embodied by Lord Asriel (James McAvoy) and Mrs. Coulter (Ruth Wilson). Debuting in His Dark Materials season 1, episode 1, "Lyra's Jordan", Mrs. Coulter took Lyra under her wing as a fledgling assistant. In truth, however, Mrs. Coulter was Lyra's mother. It also came to light that she was responsible for the abduction of countless children, including Lyra's best friend: Roger. Lyra was ultimately successful in escaping Mrs. Coulter's grasp and shutting down her brutal experiments. Regardless, Mrs. Coulter clung to power within The Magisterium and several questions about her were left unanswered. Primary among them was just how she was able to be so far away from her daemon. A prevailing theory was that Mrs. Coulter had been severed, like those in her experiments. However, His Dark Materials season 2, episode 2 might have suggested another option.
During His Dark Materials season 2, episode 2, "The Cave", The Magisterium questioned a liaison to the witches. As they did, a ritual was mentioned, stating that witches come of age by venturing to a realm that daemons cannot enter. The result is that, after the trial, witches and their daemons can travel great distances from each other without completely severing the link. Curiously, however, the camera lingered on Mrs. Coulter, who seemed to be visibly shaken by the mere mention. Given that the ritual is said to be a painful one, it could be that Mrs. Coulter underwent such a ritual and was having something of a traumatic flashback at that moment.
The reveal would support her belief that the experiments were actually a good thing - since, in her view, she'd be sparing children the pain of what she went through with a quick and decisive process. Secondly, it would deepen the conflict that has raged within her. Though Mrs. Coulter initially seemed steadfast in the Magisterium and her goals, they have been largely waylaid since meeting Lyra. More than once, Mrs. Coulter has become overcome with emotion and increasingly unable to keep her focus on anything but Lyra. In short, it could be argued that a sense of humanity has been sparked and has been steadily growing. A consequence of that would be pondering the past and dwelling on mistakes that were made. It was clear that Mrs. Coulter sacrificed a lot of herself in order to further her career. Before, the bulk of that was exemplified by giving up Lyra. However, it might also be her own witch heritage that she surrendered and buried - after a lifetime of being told it was sinful.
That would explain why, also, her choice of outfits in His Dark Materials season 2 have had flourishes tied to nature and generally echoed the style worn by witches. Since rediscovering her humanity, Mrs. Coulter has increasingly rebelled against the Magisterium. Accepting (and even embracing) her witch heritage would merely be the other side of that same coin. The books themselves never really offered an answer to Mrs. Coulter's abilities. As such, the show has free reign to unfurl Mrs. Coulter's backstory entirely in its own way. If this was the direction the show has opted to take, it would indeed be an interesting one. Plus, it would continue His Dark Materials' trend of expanding upon unexplored parts of novels - like it had been intending to do with the next steps of Lord Asriel's quest.