Katara always keeps lilacs in their garden (and when she moves South, she uses the fortune her husband gave her to build herself a hothouse).
She smiles whenever she sees them, for they are her own private reminder, even if they are the most populous flower she cultivates, and she spreads their blooms through-out the house for the precious first weeks of spring.
At first, in this "second chapter" of her life, everyone assumes she chooses them for how they symbolize spring.
She did just win a war, save the day, land the hero. Lots of "refreshment" there.
In addition, everyone assumes that, having come from "constant winter," she loves spring, and seasons. They assume she prefers her days with constant, even hours.
(She doesn't, of course. But she has things more valuable and honored than what she left behind. The trade, not even perhaps, is a fair one.)
Then everyone - Aang included - starts to assume she loves lilacs because they stand for first loves.
They're correct, just wrong on who that love is.
When she's a widow, in her "third chapter," having vowed to put an icicle through whomever decided to divide her life into thirds based on men, Katara is merely a traditional widow. Lilacs have always been their flower.
Katara picks a fresh bloom from her hothouse, and slowly makes her way back into the kitchen, to place it with honor above her sink.
"They" have always been wrong.
She never needed lilacs to remind her of spring, then or now, and there are three children running around to remind her of Aang. Flowers are unnecessary for that, and have always been. She has no regrets about that, or about anything in her life.
Katara has always kept and cultivated lilacs, with their vibrant and quick bloom, to remind her of a boy now a man with a star-shaped scar taken for her. Her first partner, fighting by her side in an automatic place of respect, seeing her as his equal. He taught her what to expect from love, what to demand from her husband, and how some things should not be given up, even for those we love.
Maybe in this universe, in this life, Katara's first love was not her last.
As she twists the vase of lilacs just so, making the sunlight stream through the petals, Katara hopes there's a life or a universe where it was.
