Spoilers! A certain characters eyes

[Ashkendor]

Also I think Minfilia might have sabotaged the spell, causing it to spare Y'sholta's aether but take away her sight as the "toll" through the lifesteam.

I don't really think Minfilia would know how to tamper with Y'shtola's magics in such a specific way. Y'shtola cast a forbidden spell out of desperation and attempting to mess with it at all could have completely unforeseeable (and disastrous) consequences.

Minfilia may have the Echo, but ultimately she's a bureaucrat, not a mage.