The portion of the sentencd "adressed to my sister" is a PAST PARTICIPIAL PHRASE. Past participial phrases contain a verb in the past participle, in this case "adressed" and a modifier. This type of phrases function as an adjective because they provide extra informagion about a noun, in this case the "package".
None of the other options are correct because there are no adjectives, adverbs or infinitive verbs in the phrase given. It is not an elliptical clause because there are no words left out.
