When Denin brought home the injured Serin, Brii noticed his belongings were too expensive for his appearance and assumed he was a deserter or a thief1. So, as the expenses to care for Serin mounted, she had few qualms about selling his belongings (including the edgeless Sword) to pay for them.
However, as Serin regained his strength, his gentle manners and helpful attitude eventually softened her view. When Alpman scouts arrived in Mannidell to collect stragglers from the fire, she averted attention from Serin by implying that he was Denin’s diseased nephew.
1 As Serin learned much later from Denin.