I could not help myself to having break out near the point of crying. It was emotionally poignant episode, because makes her resolve amidst a rain of tears that she won't be interfering between Hiro and Shouko.
The theme revolving around the episode deals literally about newly grown-up birds who take their first flight out of the nest but first experience confusion and fear as do not know to which direction they should head for.
I would have felt the same if I was on Karada's position. Leaving the safety of home to make your own life all of a suddenly in a different town where everything is foreign to you, and you're unknown to everyone without having any friends or acquaintances to lend you a hand; all by yourself.
I have never felt bothered by Karada's naivety, in fact, it was a natural reaction for her first time in the big city. What dissappoints me about her is her natural tendency to commit self-sacrifice for the sake of the others (more specifically Shouko and Hiro) happiness.
I strongly believe that the solution should just openly communicate with each other about why they carried out those choices in the past.
Karada's loneliness and isolation was best accentuated or heightened through the use of the flashbacks regarding her parents and how their death called the destined meeting for her and Hiro to welcome each other for the first time. It was more appropriately dramatized with Karada alone and by herself on the park without a place to go, feeling the cold of the rain, and thinking about what she left behind.