Before anyone says it, she was never specified as a man in the japanese version.

That was just an insult thrown out by her older sister that Mario took seriously and wrote down (he's the one writing the entries after all, he makes mistakes).

So she's not a guy! Put your efforts on trying to figure out Chroma from Soul Eater's gender.

You got proof to back this claim? A link verifying this because if not, it's just a genderswap and nothing more.

I've heard something akin to this myself. In fact, most of the initial translations I read way back mentioned nothing about Vivian's gender.

Gender arguments are banned. Please do not continue this.

exactly, let's go with the logical solution. S/he is both

Pixiv seems to generally agree that Vivian is (usually) male, judging by the posts there.