I actually kind of liked the ending. It kind of leaves it open ended whether they'll see each other again, but with her starting to see some beauty in the world around her, it's definitely a possibility.
Now, I don't really like her sister, but she's not completely wrong. A big part of her inability to see anything good in life comes from herself. Of course, her sister's not really doing anything to help her with this, unlike Chiharu.
That said, I wouldn't mind if the epilogue told a bit more about what happens next. Like, does she start talking more with her mom or classmates? I'm actually more interested in seeing this than I am in a reunion with Chiharu.