Season 3: Ellis Grey
It's no secret that Meredith has beef with both of her parents. In season 3, we get a more nuanced view of her relationship with her Alzheimer-stricken mother (Kate Burton), who becomes lucid briefly and angrily comments about how mediocre Meredith has become. Anyway, Ellis eventually dies, but before she does, she visits Meredith in her dream state and tells her that she's anything but ordinary. Kate Burton even got an Emmy nomination for her role as Mama Grey, so yeah, she's a pretty big deal.