The Honourable Chellis Bel-Osanda is the Proconsul of Fengrir, an Imperial Combine planet which was visited by Maber Castigon in 3745 ELC.
While Castigon was present on the planet, Bel-Osanda hosted a reception in honour of Ambassador Ohl Ain of the Lem Bataan Confederation, and his attaché, Doctor Irim Su (→SFTD).
It was during that conference that Castigon killed Shard Ider Firenz, and severely injured her counterpart Mostrum Appatine. They had believed either Bel-Osanda or the ambassador to be Castigon's target, and being there to protect both her and her guests they remained in harm's way.
Bel-Osanda herself was not Castigon's true objective, and she was not harmed during the encounter.