Really, her biggest mess up was marrying into the wrong family, but that doesn't excuse her disdain towards Harry, her cowardly decision to sacrifice Snape should Draco fail at his assigned task of murder, or her ability to constantly comply with her husband even though she has her own wishes. Really, her love for her son over her loyalty to the Dark Lord is her biggest failing but also the only thing that makes her the tiniest bit admirable. She's choosing to go against the scariest dude on earth in order to save her child, which makes her a good mother. Still, it's a recipe for disaster from the start. She should have kept her nose out and her mouth shut and joined Harry in the fight for the light.
I love Stephen King and music festivals; I eat my toast upside down; I daydream about getting married probably a bit too much; and I wish every day for a pet sausage dog puppy (who never materialises – sob).