adding titles to auto sidebar menus

Hey guys, I’m using this code you gave me on another site, but this site has some third level pages and, when I’m in one of those third level pages, the sidebar menu title changes to the parent of those third level pages — I need it to stay as the title of the section; the top level nav item; much more standard. Here’s the code that goes in the functions.php via my child theme….

<?php

function avia_sidebar_menu($echo = true)
    {
        $sidebar_menu = "";

        $subNav = avia_get_option('page_nesting_nav');
  
        
        $the_id = @get_the_ID();
        $args 	= array();
		global $post;

        if($subNav && $subNav != 'disabled' && !empty($the_id) && is_page())
        {
            $subNav = false;
            $parent = $post->ID;
            $sidebar_menu = "";

            if (!empty($post->post_parent))
            {
                if(isset($post->ancestors)) $ancestors  = $post->ancestors;
                if(!isset($ancestors)) $ancestors  = get_post_ancestors($post->ID);
                $root		= count($ancestors)-1;
                $parent 	= $ancestors[$root];
            }

            $args = array('title_li'=>'', 'child_of'=>$parent, 'echo'=>0, 'sort_column'=>'menu_order, post_title');

            //enables user to change query args
            $args = apply_filters('avia_sidebar_menu_args', $args, $post);

            //hide or show child pages in menu - if the class is set to 'widget_nav_hide_child' the child pages will be hidden
            $display_child_pages = apply_filters('avia_sidebar_menu_display_child', 'widget_nav_hide_child', $args, $post);

            $children = wp_list_pages($args);

            if ($children)
            {
$default_sidebar = false;
				$parent = get_the_title($post->post_parent);
				$parentlink = get_the_permalink($post->post_parent);
                $sidebar_menu .= "<nav class='widget widget_nav_menu $display_child_pages'><ul class='nested_nav'>";
				$sidebar_menu .= "<h3 class='widgettitle'><a href='{$parentlink}'>$parent</a></h3>";
                $sidebar_menu .= $children;
                $sidebar_menu .= "</ul></nav>";
            }
        }

        $sidebar_menu = apply_filters('avf_sidebar_menu_filter', $sidebar_menu, $args, $post);

        if($echo == true) { echo $sidebar_menu; } else { return $sidebar_menu; }
    }

?>

For example, on http://besanthill.wpengine.com/academics/sustainability/calendar-and-news/ (hosted on WPengine) (hosted on WPengine) the menu title should be Academics, not Sustainability Education.

Would you mind showing me what I have to tweak to achieve that? I’m including ftp credentials for you.
Thanks!