User Role Capabilities

You need to customize file inc/class-wpsm-table-maker.php

find

public function add_menu_items() {
		$this->page_hook = add_menu_page( __('Table Maker', 'wpsm-tableplugin'), __('Table Maker', 'wpsm-tableplugin'), 'manage_options', $this->page_slug, array($this, 'print_page'), $this->base_url . "/img/icon.png" );
	}

change there “manage_options” to “manage_categories”

I don’t like to edit plugins directly since when you update, the edit goes away. Is this something I can do in child theme functions or in a user capability plugin?

No, you can’t do this changes from theme. I don’t update plugin very often, so, you can make this change