She stood there motionless, her eyes filled with tears—whether of shame, frustration, or grief it was difficult to tell.  

参考译文:她一动不动地站在那儿，眼睛里充满泪水是否羞愧，沮丧或悲伤，很难辨别。

请问老师句中的of是什么成分，什么意思？此句中的 of 是否是省略后的结构？

whether (they were the tears 省略 )of shame, frustration or grief , it was difficult to tell