How to use query_posts in functions.php

I have a shortcode I created in the functions.php of my child theme. I have it set to query a specific category. I know there is a post in the category, but it keeps returning an empty query. Here’s the code:

[Code moderated as per the Forum Rules. Please use the pastebin]

Am I missing something here, or is there a different way to do this in functions.php vs in a regular template file?