。
She must be from the south.
Literal
She [topic-は] south-region from-origin [must-be-に違いない].
~に違いない ('must be ~,' literally 'there's no doubt that ~') expresses confident inference. 南部出身 is a noun phrase: 'south-region origin.' Note that 出身 is a noun, used like a predicate adjective; 南部出身だ would be 'be of southern origin.'