Space in between gallery rows

You will need to start customising your theme’s CSS – possibly via a child theme. Try using Firefox with the Firebug add-on for this kind of CSS work.
https://getfirebug.com/

It is a child theme with customized CSS and I’ve tried adding several different things to the .gallery files but nothing has worked.

Perhaps try:

.gallery .gallery-item {
  margin-bottom: 10px;
}