Sie isst zufrieden frisches Obst.

In German both “she” and the polite “you” are written Sie with a capital S. You distinguish them by the verb form:

• Sie isst uses the third-person singular of essen, so here Sie must mean she.
• The formal “you” would take Sie essen (second-person plural form of the verb).

Obst (fruit) is an uncountable (mass) noun in German. With mass nouns you often omit the article when speaking generally:

• Ich esse Obst. (I eat fruit.)
  When you add an adjective without an article, the adjective takes the strong inflection (no article → strong endings), hence frisches Obst.

Here zufrieden is used as an adverb of manner (how she eats), not as an attributive adjective. German adverbs typically follow the conjugated verb:

• Sie isst (verb) → zufrieden (adverb) → rest of the sentence.

Obst is pronounced [oːpst]. Key points:

• The O is a long [oː].
• bst is pronounced [pst], so you hear a crisp [pst] cluster at the end.

Yes, but then it gets an adjective ending and appears before the noun. For example:

• Der zufriedene Kunde (the satisfied customer)

Here zufrieden is an adjective, not an adverb. In your sentence it describes how she eats, so it remains an adverb after the verb.