she has a fortune stashed away in various bank accounts.

stash away
是一个固定的,动副结构的短语,不是说那个stash是不及无动词,否则没有被动了
原句=
she has a fortune which is stashed away in various bank accounts.
stashed是过去分词修饰fortune,这个理解对
away 我觉得不存在什么修饰关系
就相当于,look after,本身就是不可分割的短语,不能说after 修饰谁