This comment is perfect. I think my frustration is that because Snape is a major character in the series and winds up being the anti-hero of it all, there's a great deal of consideration, discussion, and understanding he gets. While there's very little of that dealt to Petunia's character, and as a result, she's frequently treated as just awful for no good reason. The only thing I'd add to your comment, I'm sure others have already pointed out, and that's that in addition to everything you said about Petunia, after all was said and done, in the end she wound up losing Lily to the very thing that separated them to begin with. I loved in the movie how there was that glint of tear in her eyes when she was ranting to Harry about how his parents really died. "And then what did she do? She went and got herself blown up!" You can really see the hurt creeping under that rage - it's very complex moment.