She seemed pretty angry with Xander when he's was talking to her at the end of her last moments as Dark Willow, like she was resiting him maybe becuase he was partly to blame for Tara's death even though she didn't admit to his face. Xander blame himself for Tara and Buffy get shot and he openly admit to Anya when she said "none of this would be happening if it weren't for you." Even though she was gtalking about their realationship, Xander opened up to her and said he blamed himself for Tara and Buffy getting shot: "You think I'm the hero of this piece? I saw the gun. Before Warren raised it, I ... I saw it, and I couldn't move. He shot two of my friends ... before I could even.... You want me to know how useless I am? That it's my fault? Thanks. Already got the memo." So knows, maybe Willow did secrely blame Xander as much as he blamed himself, maybe even more.