Is Emilia stronger than the Four Generals? 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.