Mika never really had any friends due to her crabby attitude, she actually met all of her friends through Mila.
She's very insecure, she doesn't blame anyone for favoring Mila over her. Mila is easier to get along with.
It's hard for Mika to bite her tongue and think of way to say her thoughts nicely or at least sugar coat it.
She's actually surprised that Nico had interest in her and willing to date her. She thought he was just joking... just like all the other people.