Disclaimer: I do not own any of the characters/places/etc. Everything is J.K. Rowling's.
The first time she sees him, she is ten years old, crying in King's Cross because she was the only one not going to Hogwarts. She can't really see him through her blurry eyes, so all she remembers later is dark hair and green eyes.
The second time she sees him, he's back from Hogwarts, and she's so, so excited to see the Harry Potter. He's nothing like what she imagined the person who defeated You-Know-Who would be like—instead, he's quiet and unassuming, and yet she finds herself blushing whenever she sees him. She's only eleven, but eleven is just old enough to dream of princes, and he is hers.
Then, one midsummer night, she wakes up and Harry is at their house—to stay for the rest of the summer! She can't seem to form coherent thoughts, let alone words, around him, so she stays mute, nervously stealing glances at him.
She gathers up the courage to send him a Cupid dwarf valentine, but he obviously doesn't like it. She decides to get over her painfully hopeless crush for good, and seems to be making progress, as she's able to talk to Harry normally by the end of the year, after the whole Chamber of Secrets fiasco.
The Yule Ball rolls around, and she desperately suppresses her hopes of being asked by Harry. When she hears that he's asking Cho Chang, her heart sinks, even as she tells herself that it wouldn't have been her anyway. Neville asks her, and she accepts miserably, thinking that at least she'll get to see Harry at the dance. And then, when Ron brings up her and Harry going together, and she has to reject the idea, she's more disappointed than she was when she found out Ron was leaving for Hogwarts.
She dates Michael Corner, more to prove to herself that she's over Harry than anything else. He's an insufferable prick, though, so she moves on. Dean is cute, and he's nice, but she knows deep inside that part of her wants Harry to see her with his friend, wants him to get jealous for her, even though she knows it'll never happen. It's okay, though. She has Quidditch and she has her friends—she doesn't need Harry to be happy.
She develops a tentative friendship with Harry, one that slowly grows stronger. She's so, so happy to even have this, and she knows it's pathetic but she can't stop herself. Every minute spent with Dean just seems more and more of a waste of time, and that shove in the common door is the perfect excuse to get into a big fight and finally ditch him.
She's so happy about the Quidditch win, even though she was worried sick about Harry the whole time. Then he shows up at the party, and the impossible happens. Her world stops.
And then it starts again, except this time everything is brighter, everything is better. She's heart-poundingly happy, and sometimes she still can't believe that he loves her just as she loves him, that he's loved her for a while.
When he leaves, her world stops again, and everything is gray now. She's constantly scanning newspapers and magazines for news of him, desperately dreading the day his name shows up. If something happened to him—it hurts just thinking about it.
Then, there's the war, and Fred dies and a little bit of her dies with him. She doesn't know how much more she can handle, how much longer before she reaches her breaking point. He's finally here though. He envelops her in a warm hug, kisses her forehead. He's back, he's safe, he's here. "I promised myself that if I was lucky enough to get out of this alive, I was never leaving you alone again." "Good."