A random thought has just occurred to me, so I thought I'd throw it out there.
What is Commander Sela, instead of being the daughter of Tasha Yar from an alternate timeline, was actually that Tasha Yar? She was captured at Narendra III where a high-ranking Tal Shiar officer noted her different uniform and advanced tactical knowledge, and had her transferred to a specialist facility. There she was placed in stasis whilst her mind was probed for information before beginning a programme of brain washing, only to be revived a couple decades later as a new operative to be used against Starfleet, in particular Picard and the Enterprise.
What is Commander Sela, instead of being the daughter of Tasha Yar from an alternate timeline, was actually that Tasha Yar? She was captured at Narendra III where a high-ranking Tal Shiar officer noted her different uniform and advanced tactical knowledge, and had her transferred to a specialist facility. There she was placed in stasis whilst her mind was probed for information before beginning a programme of brain washing, only to be revived a couple decades later as a new operative to be used against Starfleet, in particular Picard and the Enterprise.