I'd like to start saying that annoying younger sister is a myth. It's always the big sis who annoys us. True story!
Haem.
So. This summer I rewatch the show. And I thought: "Dawn isn't that bad, actually".
In season 5, she's introduced as the sister who appeared out of the blue. Sure she was kind of annoying. But she was also sometimes cute. I absolutely adored when it was Tara's birthday and Dawn offered her a broom. Yes, she was Joyce's baby girl. Yes she was sometimes a bitch to Buffy. But Buffy isn't exactly always kind with Dawn either.
Joyce becomes sick. Weird people tells Dawn she isn't there, she doesn't belong here...Even her sister tells her that under the influence of a spell (she didn't know her new mission yet). Then, you learn that hey! You don't actually exist. You've been there only for a few months. Nothing is real, your memory, your life...So it's understandable that she freaks out. It's annoying that she runs away when she knows she is in big danger, but it's understandable.
I mostly liked her in the last episodes (Tough Love, Spiral, The weight of the world and The Gift). I was really touched by her speech to Spike, where she says that what happened to him, to Tara was all her fault, it wouldn't have happened if she didn't exist. I think she said something like "I'm like a ball of pain who hurts everyone". I really loved that moment. When she wanted to jump in the Gift, I think it was her way to thank everybody and to end their suffer.
So, the times she annoyed me the most in this season are...when she finds out she is the key, when her mum dies and when she is kept hostage by someone she trusted. But I forgive her because come on, those are real tough times.
(Oh and in the body, her "Where is mum?" line just always gives me the chills. It's like she immediately understood something was wrong when she saw Buffy).
In season 6, she was absolutely perfect in the first episodes. She really took care of Buffy without harassing her like the Scoobies. She begins to steal things and to go out without telling Buffy or by lying to her. Buffy also did, at her time. Remember when she said to Merrick "Is that for the lipstick I didn't pay" or something? Going out was because she was the Slayer, but still, young Buffy wasn't exactly an angel who stayed quietly in her bedroom. I'd say it's natural for Dawn to mess up a bit. I like her less when she always accuses Buffy not to pay attention to her or to be never there. Then again, it's very annoying and ungrateful but understandable in the same time. When you think about it, Dawn was seeing Buffy more often when it was the Buffy-bot than when it was her real sister who came out of the grave. (Plus, Buffy sometimes happened to bail to see Spike). Dawn's big problem here is, I think, she doesn't really have friends (apart from Janice) and Buffy's friends who are also busy. She's kind of very alone, you know? It might make her see things the way they aren't. Buffy is busy working so they still have a house. I'm not sure Dawn actually realises that. I think all she can see is that in the end, it looks like she doesn't matter, she feels left alone.
In season 7, she is more liked by many. I've read a lot "She finally starts to fight". I think she was ready to fight before, she just never was given the chance to, because she was being overprotected. In this season we see Dawn at school and see that she's a bit...Socially akward, which is really cute actually. I always thought it was weird tough. Her friend in the body isn't the same as Janice later, and at Sunnydale High she's all alone, again, she meets people in Lessons that we never see again. I always wonder "Where are her friends?". Seems like she never had the chance to know a friendship like the Scoobies have. I hated her in the "This is my house too" scene. But after that, she seemed pretty upset about what she had done.
So, I guess my point is, I use to hate Dawn, but now, I understand her better so I like her more (or say, hate her less). I think I'd always be more on Buffy's side but really now I do see Dawn's character better than just a whiny brat!