have female partners, futas and megacock kinks activated (&possibly more but these should be enough, if it still doesn't work, play with the kink settings more), know the cock growth spell, defeat her
Hmmm, that should be everything. Maybe double check that all this stuff you listed if there? Also if you don't have enough mana to cast the spell, it'll be disabled. But you'll be able to see the options listed when you defeat her
That stuff will more likely be end of route type rewards instead of something you can get just anywhere