OK... like the others, I originally was confused over why the last sentence was written "C'est un ange!" instead of "Elle est un ange!"  I now understand and accept that "C'est" is correct.  However, I want to ask a follow up question about the explanation offered.   The reason given was" With sentences that have "she is a+noun" we use C'est."  That sentence suggests to me that the key to using "c'est" is a following noun.  However, re-reading the grammar guide, my understanding instead is that it's the use of an article or determinant such as un, une, le, la, les, des, etc., plus a noun or pronoun that drives it.  I suppose it could be countered that such articles always would be followed by nouns or pronouns.  After all, were one to use a sentence such as "C'est la jolie," as I understand it, "la jolie" in that example would not just cause the sentence to translate as "It's the pretty."  Instead, in that case, "la jolie" would behave as if a subject, causing the sentence to translate to mean, "It's the pretty one."  If I am correct, then my issue may be a moot point.