Underground
Aelina left the Crimson Slayer Sect without ever asking about Mira. Of course, there was a good reason for this. For one, that wasn't the reason she made this little trip. No matter how talented Mira was, that's all she was: a talent. Sure, her potential is limitless, but until she reaches that potential, she's just like every other disciple.
If she had to leave the Sect to confront every person who dared to kill one of her disciples, she'd never be free!
Sure, she can order the other elders to go in her place, but why should she do that to them? Most of them are busy cultivating, researching, concocting, creating, or on some other mission, she's already given them.
They don't have time to take care of every casualty in the Sect, nor should they have to.
Now, if Mira were a Core Disciple, Direct Disciple, or Elder, that'd be a different story. Everyone who possesses one of those titles is unique and irreplaceable to the Sect.