I guess my read is, in the cafeteria scene, she's acting to protect herself. She's only going to be there for six months, and she just doesn't want any drama. And I don't see anything wrong with that!

But if you look at her life as a whole, it's like she retains that attitude the entire time -- she's not going to let anything affect her or matter to her, not in any kind of deep or lasting way. Which has the effect not only of ruling out cool things like friendship, but also of allowing her to say with impunity that she doesn't care about anything that doesn't impinge on her personally.

So while not really being a joiner isn't in itself a bad thing, in Eleanor's particular case, it is related to her own unique brand of terribleness -- just like Tahani's compulsive networking is for her.