The places where Becker Solis's lore intersects with Andrew's have been extensively discussed with the Millenials, so I think I've gotten everything to match.
Origins: Becker Solis followed her older brother Andrew Solis through the dimensional gate he disappeared into. It almost worked, but it landed her in the Shadows. Becker was immediately recruited by the Agency, and became a globetrotting superspy. In between jobs she researched where her brother was, and how to leave the Shadows.
Emergence from the Shadows: As Shadows transactions became more and more prominent in the Elections, Solis eventually figured out how they worked. When Wills became a thing, she planned to unshadow herself when the time was right... but she realized, in Season 14, that Foreshadowing might not be available in any future elections. She wanted to reunite with her brother desperately enough that she forged the paperwork that would let her leave.
Relationships/Reunions: Solis realized, too late, that she had accidentally shadowed Fitzgerald Blackburn, and that she might have taken Bailey's only remaining chance to re-emerge. She has admitted to this and apologized; not all of the team have forgiven her. On the other hand, she remembers Emmett Tabby from her time in the Shadows, and likes (or loves?) Jomgy Rolsenthal.
Her reunion with Andrew was rather more fraught; even in the timeless time of the Immaterial Plane, twenty years have changed them both. He thought he'd lost everything when he left. She realized that Blaseball had left him scarred. But they managed to reconnect.
