Where you took that from? First of all she’s usually focused on other gods if you follow Homer story. Her daughters are more focused on humans 
Not exactly, that is modern concept, discordians like to present. She is goddess of discord. Discord is very useful. If you want to win over a united group or clique you can wish to make discord among them, so they become weaker.
Divide et Impera
Discord is very useful strategy in media, war, business and politics. And among the trolls. I see many reasons to work with Eris. Just because she doesn’t fit our idea of comfort it doesn’t mean she’s not beneficial in her way.