However, that's also a plot point that got resolved long ago. Siuan went from taking advantage of the situation to a mea culpa and regrets. Egwene and her had this long conversation about the Oaths in which Siuan made very clear she couldn't wait to be bound by the Oaths again, and would retake them at the first occasion.

There wasn't much point to show her doing this on-screen. We already got the scene where all the rebel Sitters did.

We knew Siuan wasn't Black, and it's clear Siuan never intended to find a way not to be bound by the Oaths ever again, when she's the one who convinced Egwene to abandon her notion of getting rid of the Oaths.

I could see why Jordan might have wanted to show this on-screen if Siuan/Leane were the only ones retaking the Oaths (whether they did so secretely or admitted they have been freed of the Oaths after stilling), but as it happened during the BA purge and every sister swore the Oaths, there was really no point in having a scene where Siuan did it. To show us what? That she was relieved/happy to be bound again? From her conversations with Egwene, we already know that's exactly how she'd feel about it.

The series is big enough as it is, it can't really afford extra scenes we already have all the information to imagine for ourselves.