Emphasis. "Corinna sum" would be the standard, neutral sentence. Changing the order changes the emphasis, and adding the pronoun adds emphasis.
The pronunciation of the R in Corinna is wrong, it should be rather modern Italian than English.
Please report audio issues using the button in the lesson, not in the sentence discussion.
(I reported most of the cases using the report button, though I can't remember whether I have reported this very case. As for the audio in general, both narrators don't sound Latin, if you can, please find some pholologists from Italy to re-record everything)
That's context dependent. It would be the standard, neutral sentence, but the order can be changed and the pronoun included for emphasis.