Throughout Season 3 of 'The Umbrella Academy', Allison is too vicious towards Viktor. It looks like her brother did something terrible to her, for which she wants to punish him.
Allison's hate towards Viktor has been a subject of massive fan speculation. Most viewers are sure that Allison holds her brother personally responsible for the fact that they are stuck in an alternate reality they were not born in. For Allison, this means that her daughter Claire was never born. Allison's husband is not in this reality either, so basically she lost everything she held dear in one day.
This is a lot to blame your brother for, but, as 'The Umbrella Academy' fans are speculating, Allison should rather blame not Viktor, but the chain of events that led to her daughter no longer existing, and Allison's husband left in the past.
Yes, Viktor lied to her, but that's not nearly as much as Allison wants to blame him for. Fans believe that because Allison's pain is too strong, she just needs to find someone to blame for the fact that she lost her family, if only as a defense mechanism to cope with grief – although it actually looks like she's already lost her mind a little, as some viewers mention.
In addition, Viktor chooses to help Harlan while completely ignoring Allison and her family. Of course when she finds out that Harlan was responsible for the deaths of the Umbrellas' mothers, Allison hates Viktor even more. Fans note that although they do not justify Allison's actions, it's actually understandable why Viktor looks like the culprit of her problems in Allison's mind.
"I felt her venom to Victor was over the top. I get it. She lost her daughter. Again. However. It wasn't really Victor's fault IMHO, and Allison literally RUMORED Victor as a child and ruined their entire LIFE. And rumored her own kid. More than once she admitted. Until she got busted by her ex. And the dream team is trying to fix the timeline so she can get back to her daughter. Who she's not allowed to even see. IDK. I'm team Victor and Five and screw the rest of them." – /Leesababy25
But some viewers noticed that the list of things Allison can hate Viktor for goes on. The fact is, she is left alone in her grief, with her family ignoring her pain. At that same time, everyone supports Viktor. Naturally, this infuriates Allison even more, because no one gives her such support as they give Viktor. This is illustrated by something Allison told Viktor once:
"This whole family is so quick to tell me to suck up my pain and so worried about fixing yours. Someone had to pay... because you never seem to."
There are even more reasons for Allison to hate her brother. After all, it was because of him that she was stuck for a year in racist Texas in the 1960s. This adventure clearly did not please Allison, because she was used to having a voice — both literally and figuratively.