is it correct if I say "she mustn't be at home."
in chinese-english grammar educiation, we shouldn't use the sentence like the topic to express the indication that you are fairly sure that something is the case. we should use the sentence " she can't be at home";
I think "she mustn't be at home." can mean the similar meaning.
Is my thinking correct?
thank you very much.

Question

is it correct if I say "she mustn't be at home."
in chinese-english grammar educiation, we shouldn't use the sentence like the topic to express the indication that you are fairly sure that something is the case.  we should use the sentence " she can't be at home";
I think "she mustn't be at home." can mean the similar meaning. 
Is my thinking correct?
thank you very much.

Answer

Remember that can and must are modal verbs, and you use it according to the context. If you are speaking properly, then you use must. And if you are speaking in an informal context, then can is the best choice. Anyway, I think that "She must not be at home" is correct if the circumstances require such a formal way to say it.

Answer

Yes.  In fact the most common form you will hear in English is "She must not be home."  Note that you may omit "at," which is understood implicitly.