Harry Potter and the Chamber of Secrets
Ginny Weasley is Ron's younger sister and the youngest child in the Weasley family. She is also the only girl. We don't get much of a sense of Ginny yet, primarily because she has a giant crush on Harry. As a result, she can barely muster up the courage to speak to him. Since he's our main character, that leaves Ginny mostly off our radar until the end. Yet, while we may not hear much from Ginny directly, Chamber of Secrets definitely includes hints that she's going to be important later on in the series.
First of all, while Ginny does have this massive crush on Harry, she is also brave enough to try sending him a singing Valentine: "I wish he was mine, he's really divine,/ The hero who conquered the Dark Lord" (13.103). Some have guessed that she might have been forced to do so by Voldemort to humiliate her, but nope. When a fan asked J.K. Rowling if it was Ginny who sent the Valentine, she answered, "Yeah, bless her" (source). So Ginny has a lot of pluck – even if she's a terrible, terrible poet.
A less lighthearted sign that Ginny is made of tougher stuff than it initially appears comes at the end of the book, when we find out that she has been the one Tom Riddle has been using to terrorize the school. She doesn't manage to free herself from his control by herself. Yet, we have plenty of evidence that she fought him with all her might. She tries to flush the diary down Moaning Myrtle's toilet, and she also steals it back from Harry once he finds it, even though there is nothing Riddle wants more than to stay in the hands of Harry Potter. Ginny may fall victim to the diary's soul-sucking powers, but she doesn't just stay passive and let Riddle possess her: she fights back hard for most of a year.
Ginny's strength of character in fighting against Riddle's influence is supposed to shine through in Chamber of Secrets. Rowling has commented [WARNING: Book 6 spoilers ahead!]:
[T]he plan was, which I really hope I fulfilled, is that the reader, like Harry, would gradually discover Ginny as pretty much the ideal girl for Harry. She's tough, not in an unpleasant way, but she's gutsy. He needs to be with someone who can stand the demands of being with Harry Potter, because he's a scary boyfriend in a lot of ways. He's a marked man. I think she's funny, and I think that she's very warm and compassionate. These are all things that Harry requires in his ideal woman. But, I felt – and I'm talking years ago when all this was planned – initially, she's terrified by his image. I mean, he's a bit of a rock god to her when she sees him first, at 10 or 11, and he's this famous boy. So Ginny had to go through a journey as well. (source)
In other words, Ginny is extremely important to Harry's life, but she can't take center stage as a major character right away. She and Harry both have to grow into the people they become by Books 6 and 7, when they finally begin to acknowledge their feelings for each other. So, when Ginny is introduced in Chamber of Secrets, she seems mostly like a nice kid with a crush on the Boy-Who-Lived. There are hints of her deeper character in Book 2, but only hints.