According to the Hataraku Maou-sama Wikia,
Satan tried to conquer the land of Ente Isla with four of his war generals, Adramelech, Lucifer, Alsiel, and Malacoda, but was eventually forced to retreat to Earth due to the interference of Emilia and the resisting human armies.
If this is true, it is possible that she can beat Maou-sama. (Though that was in Ente Isla). Does this mean that Emilia is stronger than the Four Generals?
Maou has been around for over 3 hundred years and has been taught more magic then even alciel knows. Emi has half human blood in her, so even though she can fly, heal, knock out someone, and use a sacred sword, she could not win in a fight against the demon king. The only reason she was able to corner him was because she had her comrades with her.
That is true satan is a true demon with immense physical prowess and demonic powers. well humans are immensely weak since emi is half human she could and won't be able to defeat satan. Maybe if she was a full angel she might be in equals term with him.
When it comes to Powers and Abilities , Maou had a great power than Emi . As the Demon Lord, Maou possessed great demonic power. Demonic magic is extremely strong, and each user seems to have a unique coloured aura to indicate its presence. For him, that color is black.
On Earth, he lost most of his powers and was weakened to the point that he could only function as an average human. Finding magical sources was near impossible as magic is largely only present in the form of fiction. However, his powers can be temporarily restored by feeding off negative emotions like fear and despair from sentient beings in the surroundings, such as during the battles with Lucifer and Sariel.
Maou is able to cast so many high-class offensive and defensive magics to attack enemies or to defend himself from harm with ease.
Maou is surprisingly intelligent, able to piece events together and form a logical conclusion with relative ease, such as when he figured out Lucifer's motivations for the mugging incidents around the neighbourhood to accumulate power.
While Emi's human body is more fragile on Earth than it is in Ente Isla ,shown to be capable of flight, but its limitations (such as whether it uses up her Sacred Power or not) are not clear as of yet.
to be exact Emi can't defeat Maou.
