Real talk that demon army doing it all wrong. If they know right off the bat the bimbo waste of a deity is going to turbo buff the humans than you need to turbo debuff them. Not magic or curses, nah. Show up with 10,000 orcs and goblins and plaster "viagra" on every single supply crate. Then at night (or day since the hyumans attack at night) just have someone magically project their voice.
"Man you hyumans really are beautiful!", "I can see why your goddess prefers beautiful women! We do too.", "you know I knew this hyuman chick once. She kept talking about something called 'pulling out' do you know what that is? (Orc grumbling and goblin cackling followed by announcer loudly grunting) yeah me neither."
Morale is irreplaceable to an army, so shatter their will to fight along with their pride in their beauty and it doesn't matter how many buffs the dung beetle goddess gives, they'll fold like a deck of cards. Best part? It's all taunt tactics, you don't actually have to dirty your hands, err "hands", you just have to make them think you are meanwhile you're getting actually strong fighters to flank and use guerrilla tactics like hit and runs, sleep deprivation, traps, camp raids, poisoning supply lines, etc. If they aren't clinically insane by the first week you aren't trying hard enough.