Early on, Sir Reginald discovered that her emotions were linked to her ability to harness sound and convert it into energy. Despite trying to teach her to control them, he deemed Vanya's powers to be too great and destructive to ever be let out. As a result, Sir Reginald worked to cover them up and suppress them.

What is wrong with Vanya in Umbrella Academy?

At the end of season one, Vanya (Elliot Page) lost control of her powers, blew up the moon, and caused the apocalypse. But with Number Five's (Aidan Gallagher) ability to transport through space and time, he was able to help the siblings escape.

What did Vanya do that was so bad?

Though she kills multiple people in pretty gruesome ways, it's impossible to categorize Vanya as evil given all that she's been through. ... She kills Leonard after discovering that he was using Sir Reginald's journal to manipulate her. And she causes the apocalypse after the Umbrella Academy tries to subdue her.