After Vaan finished his self-evaluation, he shifted his attention back to Henrietta, who was nearly done condensing her eighth mana ring with Empyrean Scarletsea's help. As he observed Henrietta's advancement, he realized a few things based on the staggering amount of mana consumed.
Firstly, despite possessing a cheat-like existence, such as Empyrean Scarletsea, to aid her cultivation, Henrietta could not progress further than the Early-stage Transcendent Witch rank. That was because there was never enough mana to keep up with her consumption rate in forming new mana rings.
That said, given Henrietta's status and power, accumulating the necessary quantity of mana for her advancement shouldn't be impossible.
As such, it wasn't that she couldn't advance; she simply chose not to.