>>150859714
It's just plain social anxiety. Otherwise she's just settle into whatever 'Nerd' or 'AP' clique that existed at Lawndale. The fact that she doesn't shows that she fears judgement and rejection from those least likely to.
Being forced into Brittany's social circle would unironically be the best thing for her, as Brittany would automatically consider her a friend, and Daria would learn how to deal with interacting with her peers, both friendly and unfriendly alike.