You do realize that bigotry and lingering patriarchal tendencies are why women get marginalized in our modern society, yes? It's also why most medical testing is done on male subject, because all the womanly bit and hormones throw off their tests... all of which sounds completely and utterly insane for it to exist in a first world countries, yet it does. You have to look no further then the reproductive rights of women being revoked, yet again, in the US not long ago.
As for my speculation about her mother trying to prevent her daughter from causing internal family political issue, it could go many directions. The Emperor could welcome any strong member to join him in the capital, or could see it as a direct challenge to his authority. The same could be said for every other of the 13+ families in the Emperor's harem.
All we have to go OK at this point in the story is that her mother is firmly against her weight training, ruining her figure, and the perception that she is an out of control meathead with the moniker the Armored Princess.
