Literally a direct translation of "Miss Devil". This is a term used to describe the types of spanish teachers that are overly materialistic and highly judgemental - the types of things you might see in a spawn of the devil. Because Señora Diabla is so materialistic and judgemental, she comes off as highly unattractive and therefore does not have kids or a husband even at the age of 45.
It also kind of refers to the general idea that spanish is the devil's language, and therefore the spanish teacher IS literally a direct spawn of the devil.
Person 1: Yo, you see Señora Diabla roll up in her 350z? How does a teacher afford a nice car on that salary?
Person 2: Yea man but she doesn't have a husband or kids to spend her money on. All she has is her 666 cats.
Person 1: Yea dude I can't stand her she is always trying to judge me like she is God or some shit...