We were relieved to hear that she was out of danger. 这不是动词relieve形容词化，而是动词的过去分词演变为形容词，词典已经给出形容词的词性。句子为系表结构，表示主语所处的状态。如果你把be relieved分析为被动语态，则是表示表示松了一口气这个动作。例如我把这个句子改一下：

When we heard that she was out of danger, we were relieved. 这就是被动语态表示短暂动作了。

He is aching for his mother. = He is longing/yearning for his mother. 这是进行时态，不是系表结构。aching在此不是形容词。