黎老师，我有点不同的看法，不一定对，请您指教。
我认为：ask后接动词不定式作宾语补足语，即ask sb. to do sth.“要求某人做某事”。而不应是 ask sb to be done sth 要求某人被做某事。
She's asked to be left alone. 应该等于 She has asked to be left alone. 不是不定式作宾语补足语，而是作宾语。
《英语常用词用法·详解大词典》席玉虎p268：
She asked to be given more work to do. 她要求给她更多的工作。
Jack asks to be given another opportunity for the exam. 杰克要求再给他一次考试的机会。
He asked to be allowed to stay in the club. 他要求允许他留在俱乐部。
参看下面一道题：
【2013 山东济南】52. It was time for class. Mr King asked all the children _______ down quietly.
A. sit B. sat C. to sit D. sitting
【解析】选C。考查非谓语动词。句中动词为ask，后接动词不定式作宾语补足语，即ask sb. to do sth.“要求某人做某事”。所以答案选C。

感觉两种可能都有：

1. She’s asked to be left alone.

= She has asked to be left alone.

意思是：她请求把她单独留下。（ask to do sth 请求做某事）

2. She’s asked to be left alone.

= She is asked to be left alone.

意思是：（人们）要求她被单独留下。（涉及ask sb to do sth，要求某人做某事）

这个句子上下文不全，但是我个人认为 She's asked to be left alone. 相当于She has asked to be left alone. 意为“她希望不被打扰”。如果是被动，句子过于纠结，英国人说话也不会让自己的舌头打结的。

要有语境：She's (=has) asked to be left alone but the press kept pestering her. 她要求不要打扰她，可报界总是缠着她不放。