@sirflimflam It's not hard to see why people still rag on her, but I look at it this way.
When you think about it, Miya is expected to be sad, cry and grieve over her mother's death because she's a young teenage girl, so she'll undoubtedly have a lot of shoulders to cry on and gain support from her classmates and teachers. Kosuke, on the other hand, is expected to shoulder all the criticism and responsibility to take care of her, work to keep a roof over their heads and food on the table, and interact with her like everything will be ok even when he's feeling the exact same way as she does. If she wants to just up and run away, she's pretty much allowed to, and who has to shoulder the responsibility to try and bring her home and make sure she's ok? Him.
It's not that she's a selfish brat. I find that it's more that she's a bit too wrapped up in how she's feeling that she fails to see that he's also suffering as much as she is, with the main difference being that she can get away from it all while he has to stand and fight, even when he's out of weapons, ammo, and armor. We also can't forget that before Koto, he was getting virtually zero support from anyone during the early parts of the story. Even the most well adjusted adult would start to crumble underneath that kind of neglect.
But even with all of that said, I can't blame her for not helping him. She didn't know how much he was suffering, and that unintentional neglect unfortunately was a major factor that lead to the current situation.