In truth, Seina was a bit skeptical about whether or not Izroth's plan would work. However, it ended even better than she anticipated!
Not only did Seina uncover who was responsible for poisoning her disciple, but she even acquired solid evidence of Yuveil working with outsiders.
Still, although Seina was glad that she got some answers, she was truly heartbroken and deeply wounded by her senior sister's betrayal.
She knew that their relationship had deteriorated since the day her master chose her as the Holy Maiden over her senior sister, but Seina did not think it had reached such a low point.
As her junior sister, a part of Seina wanted to ignore Yuveil's misdeeds and try giving her another chance to redeem herself.
However... As the Holy Maiden of the Order of a Thousand Blossoms, Seina knew what needed to be done.
(Unedited)