Question

How does the use of alliteration in these lines influence the reader's emotions? and maggie discovered a shell that sang so sweetly she couldn't remember her troubles, and

Answer 1

An alliteration points to the first letters being the same (or same sounding) for a series of words. 

In this case "s" is the alliteration. In the English language the sound of "s" is used to hush or clam someone. "Shhhh" or "Husssssh"