What hopes did she actually have? The cookie dough speech where she pretty much doubts she'll ever live her own life beyond being just a child soldier (which she was and created more of herself)? The life she leads in the comics? Because I just see her in an endless loop of going nowhere with her life. She did other morally yuck things in season 7, as well, like what she told Spike in Get It Done (preferring the soulless him in the dead Slayer's coat to the one dealing with his guilt and shaming him to put his soulless costume and personality back on). She's been even worse in the comics. And everybody at Slayer Headquarters should be ashamed of what they did to the Fang Gang in AtS season 5 (despite the comics' desperate attempts to get the blame off Buffy because of how bad Giles and Andrew's actions are).
I don't see a lot of hope in Chosen. She might think there's hope after Sunnydale is gone, but she just did something horrible. The problem with her cookie dough speech was she doubts she'll have a human life. Young Buffy, on the other hand, used to fight back against her calling to retain every little bit of her human life she could. She even told the Council to go shove it and she was no longer their tool. While she wants to help because she can, she still had hopes and dreams before, even trying desperately to fit in normal things into her bizarre life. Sadly, she gave up most of them when Angel left. A lot of her dreams revolved around making it work out with him.
He also made her feel that some of the weight was being lifted off her shoulders because he could help her as an equal, but was also a comforting, wise figure she could turn to when she was hurting (one of the few people she really talked to about things like her parents' divorce and he was always there urging her to think about future aspirations like college and family--Angel always had a strong paternal instinct with lots of characters). He was even more so a help to her in L.A. in terms of taking care of evil she couldn't be everywhere for, given he was stopping as many apocalypses as she was. This him the most equal of any of her relationships, as he actually knew what she went through with that much stress and being the one everyone looks to to do everything.
In that regard, he failed to do what he had hoped by removing what he had believed had only made her miserable and was keeping her from the normal life she had previously always stated she wanted. I Will Remember You even reveals her lie to Angel that it didn't matter to her what he was, given she admits her fantasy was of them being normal. While he needed to set off on his own to find his own destiny and Buffy was being held back to some extent holding onto him desperately for that bit of normalcy, even if what he was got in the way of her achieving what she wanted with him. The thing is, she never really moved on and her next failures at love only reinforced how she didn't believe she was going to get what she wanted out of life anymore. Going back to a vampire relationship, even without the curse, is right back to running in place for her, while she completely refuses to face any of the reasons Angel always brought up with her for what he (and Spike) can never give her. Human relationships and vampire relationships are both dead ends for her for different reasons.
She wanted out of life in season 5, was happy she got it, loathed being back and while we get all these pretty scenes of her digging out of the dark and smiling in the sunshine, all she does after this point is more of the same; still running in place. Except she's now done what was done to her to thousands of others. She's now the Watchers' Council she had once rebuked when they ordered her around like a child soldier. She's no better than the Shadow Men she practically accused of being rapists.
The Scoobies, Fang Gang, Angel (who, like Buffy, never chose to be what he was) and Spike (with the soul, which is when he actually cared that people were suffering--getting the soul to get a girl back without regard to her feelings in the matter wasn't the noble part of what he did) chose to help because they wanted to with their eyes wide open about the risks. The Slayer spell wasn't a choice (just as being called wasn't a choice for Buffy either), but something done to the girls, who weren't prepared for the consequences and the spell wasn't indiscriminate either. How many more Danas are out there?