Timing of Midnight Mother's capture

[Hilfandor he/him]

Was listening to the Ba-Ado-Mishram Shardcast where they discussed the timeline of the Recreance and abandonment of Urithiru, and a question came to mind.

Prior to BAM being captured, the Radiants were unaware of the ability to trap spren in gemhearts. Around the same time of the capture, the tower was abandoned, because the Sibling's abilities began to fail. The Recreance, theoretically, occured shortly after.

In OB, the Midnight Mother is residing in the tower, near what I assume is the central control pillar. In fact, she had essentially wrapped herself around it. The Midnight Mother was captured by a Lightweaver in the past. The Coppermind says she escaped and chose to remain hidden in the tower until Shallan scared her away.

How did they imprison her if it was before BAM being placed in a gemheart? If it was after they discovered it was possible, how did she escape? How would the Sibling feel about having an Unmade in Urithiru (both captured and living there freely) since I don't believe it was brought up in RoW?

I know the timeline for the exodus and the Recreance is muddled, but it's a detail that I haven't seen discussed (though i haven't gone through the forum completely)

[LordTheodore]

I believe that shortly before the attempt to imprison BAM, a lightweaver successfully imprisoned re-shepir and in doing so confirmed the theory that the unmade could be trapped in gemstones.