I have just recieved a letter,informing me that she is sent to America请高手解释此句的结构,是什么从句我个人认为是和非谓语动词和状语从句有关吧，可是又有些糊涂，请高手指教了

宾语从句
从句为informing me that she is sent to America，是解释宾语的。
sb. do sth. that（可省略）....

informing me that she is sent to America是分词短语，不是从句，如果是从句的话，那应该写成：
which informs me that she is sent to America
但短语中确实是有一个宾语从句 that she is sent to America

I have just recieved a letter是主句,
informing me that she is sent to America 是非谓语,但不是从句,现在分词做伴随状语,修饰主句,表示收到信件的同时,通知了我她被送去美国了.
that she is sent to America 是非谓语里面的宾语从句,表示通知我们的内容是什么

这句话是定语从句，informing me that she is sent to America是用来修饰逗号前Letter这个名词，翻译过来就是我刚刚收到了一封来信，通知我她被派到了美国。也可以翻译成我刚刚收到了一封通知我她已被派到美国的来信。