Like with Arturia, it's only implied that she MIGHT have been a man in the first place. After all, it mentions protag thinking she might have "been raised as a boy". It's basically left up to which you prefer, like with "Sir" Francis Drake. I personally like the idea of Francis Drake actually being a busty lady pirate, same as I do Nero being a female bisexual(who wrestled a lion nude of course). Besides, she's female in this incarnation, no matter what.
Also, don't say "seibah", it makes you sound super weeaboo.