Learn Italian: Se si è isolati, non c'è nessuna distrazione. - If one is isolated, there is no distraction.

This is a special rule in Italian: when you use the impersonal si with the verb essere (to be), any adjective that follows must be plural. Even though the subject feels singular, the adjective isolati takes the plural ending.

Could I say Se si è isolate here?

Yes, but only if the general group of people you are referring to is exclusively female. When making a broad statement that applies to everyone, Italian defaults to the masculine plural, which is why we use isolati here.

Why do we need non before c'è if nessuna already means 'no' or 'any'?

Italian requires a double negative when a negative word like nessuno, niente, or mai comes after the verb. Since nessuna is placed after c'è, you must put non before the verb.

Why is it nessuna distrazione instead of nessun distrazione?

The word nessuno changes its ending to match the noun it describes, following the exact same rules as the indefinite articles (un, una, etc.). Because distrazione is a feminine noun starting with a consonant, we use the feminine form nessuna. You can usually recognize feminine nouns because they end in -zione.