I mean she lies to Voldemort about Harry’s death. FRICKING VOLDEMORT. And for what reason to gain? I don’t know.
But what we do know is that she saved Harry’s life so he defeat Voldemort. Maybe she really wanted Voldemort dead this whole time. Maybe she wanted him dead so her family was no longer under the threat of the Dark Lord. She did leave with Draco and her husband after Harry “resurrected”.
Whatever the reason, she let Harry live which ultimately let to the downfall of Voldemort. A lot of people overlook this, but I think she is one of the most important people in “Harry Potter”.