答案应填 by。year after year与year by year的区别是：year after year强调持续（=every year for many years）； year by year则侧重变化。比较：

Roses and geraniums are perennials, flowering year after year. 玫瑰和天竺葵是多年生植物，年复一年地开花。

Our salaries weren’t in fact moving up year by year as projected. 实际上，我们的工资并未按计划年年递增。

你的句子意思是：

She was getting older year by year, lonelier and more ridiculous. 她一年比一年老，越来越孤独，越来越可笑。