D. Gibbons used the fact that Demetri didn't have a flash for his advantage (which is why she contacted him so quickly). He had Nhadra contact Demetri with a false guise of secrecy, knowing that he and Mark would track her down. When they did, she would reveal that Mark is the one to kill Demetri, and this would destabilize their investigation.
She said that by coming to find her, Mark and Demetri set the future in motion (A561984). Rather than this just being an wish-wash cryptic answer (like so many others have been before), she's actually hinting that this was all a set-up.
But is her involvement with D. Gibbons voluntary? She seemed genuinely sad and angry when Mark and Demetri showed up (therefore D. Gibbons' plan worked).
If she is genuinely sad, then that may fit into the theory that her mosaic and Mark's will combine; maybe she'll do it out of contrition.