The example I gave you is 'poetic parallelism'. It is where a statement is made and then repeated in a different way. Another example,' The Lord has made known is salvation and his righteousness has he openly shown'. He is saying the same thing is both cases but in a slightly different way. See this all the time in the Psalms.When your soul magnifies the Lord, you are using your free-will to magnify the Lord. The result is the anointing. When the anointing comes upon you, your spirit will rejoice.
Thus, Mary stated, 'My soul magnifies the Lord, and my spirit rejoices in God my Savior'.
Magnifying the Lord with her soul is identical with rejoicing with her spirit. Spirit and soul are used interchangeably.