问
在 I forgot seeing her. 中动名词 seeing 是表示过去的事件(I saw her, but the seeing subsequently escaped my memory.)，由此我断定 I forgot having seen her. 是一个错误的表达方式。
答
实际上,forget having seen 并不是一个错误的形式。请看下面的例句：
I forgot having met her. (CGEL)
(参见 remember, deny)
forget
forget seeing/having seen