Yes, we know she dies halfway through the book. But she’s the linchpin of the novel! She’s a centerpiece in so many different ways. Think about her walk with Mr. Tansley, being framed in the window with James, and the triumph of her dinner. She creates; she smoothes over; she brings in harmony. Her absence in the latter half of the book merely serves to reinforce her role in the first half. Whoa. That’s like… a foil.
Wait, isn’t Mrs. Ramsay…? Oh, but here’s our argument: Mrs. Ramsay is a poster girl for "Womanhood" that Lily Briscoe chooses to reject. Lily is the true protagonist of the novel as she is the only character who actually succeeds in capturing Time: she does it by successfully completing a painting. She’s also, dare we point out, alive for the entirety of the novel, and her thoughts and recollections regarding Mrs. Ramsay are the most nuanced that we see in Part Three.
Hold your horses! There’s more: Lily is still a spinster in Part Three of the novel, confirming that she refused to bow to Mrs. Ramsay-like pressure. In fact, Lily feels freedom, relief, and grief at the absence of Mrs. Ramsay. This, coupled with the successful completion of her painting, tells us that Lily has walked the longest journey, skinned the biggest hare, climbed the highest mountain, whatever you want to call it. We call it protagonist-ation.