Seina would tolerate many things; however, threatening her disciples, who she treated and raised as her own daughters, was the same as touching a dragon's reversal scale!
That being said, even though Seina saw right through Yuveil's actions, it was still enough to make her momentarily hesitate.
If the pill truly did not heal her, then after she was gone, who would protect her disciples from those vying for power within the order?
The guardians? After her constantly declining health, the few that were on her side had switched over to Yuveil.
Yuveil's influence was already at the top among the guardians, and none of them would speak out against her. This was even more so if Seina was not around.
"After all these years... Master, why did you choose me that day?" Seina thought to herself as she closed her eyes to contemplate.
(Unedited)