well, I wouldn't rule out hormones that easily, although I'm confused how old the kitten is - from the first post I understood the cats first met at around 5 mo (brought home at 4mo, 3-4 weeks isolated)? And it's been almost 2 months since M was brought home? If I understand this timeline correctly, it's totally possible that older female could detect hormonal changes in 5mo. My own kitten’s urine started smelling funny to me when he was 6mo, and these changes are gradual, so I can imagine that cat's nose would detect any change earlier. I've seen mothers rejecting their sons at 4mo - males, but not females. I've seen 6mo female that got pregnant with her litter brother.
It's a different story if hormones alone enough would cause such a violent reaction. Probably not, but I wouldn't rule this out, as it seems she first sniffed M then attacked, and since T- I'm assuming - for the last 10 years hasn't smelled a male unneutered cat at all, I can imagine she felt threatened.
Personally, I'd never introduce intact 5-6mo male to another cat. Even if it's not direct cause of the attack, it will certainly not make things easier, and with time it will be worse and worse.
It's a different story if hormones alone enough would cause such a violent reaction. Probably not, but I wouldn't rule this out, as it seems she first sniffed M then attacked, and since T- I'm assuming - for the last 10 years hasn't smelled a male unneutered cat at all, I can imagine she felt threatened.
Personally, I'd never introduce intact 5-6mo male to another cat. Even if it's not direct cause of the attack, it will certainly not make things easier, and with time it will be worse and worse.