She was probably very antisocial, and only liked to read. She studied, and practiced magic. The only true friend she really had was her brother. I think it was best, because Shining Armor seemed fairly humble, for the ponies in Canterlot.
I did truly think that Twilight was a bit too obsessed with Smarty Pants, and the doll was the biggest friend she had, besides her brother.
Cadence, however was an exception. Considering she was a nice babysitter, she was very close friends with Twilight. Who wouldn't be friends with Cadence.