[Jellby]

You are telling that "normal" paragraphs are not indented, and only paragraphs that come after a paragraph have a 1.5em indent. You can either:

1. Add a rule to indent paragraphs that come after a poetry fragment too:

div.poetry + p {
  text-indent: 1.5em;
}

2. Reverse the rules, to have normal paragraphs indented, and only those that come after a heading indented:

p {
  margin: 0;
  text-indent: 1.5em;
  text-align: justify;
  font-size: 1.00em;
}
h1 + p, h2 + p, h3 + p { /* and more, if needed */
  text-indent: 0em;
}

3. Or add a specific class for non-indented paragraphs:

p.noindent {
  text-indent: 0;
}