This is a beautiful line about Ned Stark’s sister, Lyanna. There’s a lot weighing on the word winter. Winter for their family’s home (Winterfell) and winter for the season that most represents death. The sentence ends in a subtle clash with winter next to roses because roses (or any flower) typically resonates with spring, a season of life and new beginnings. These two words put together at the end makes for very powerful imagery that sets Lyanna as a constant reminder of the delicate line between life and death (a main theme in the series).
“She had loved the scent of winter roses.”
(p.631 in the paperback version)