Include one page/post into query which is already returning posts

And here is the correct implementation:

Register the category taxonomy for the page post-type:

function wpse121285_add_category_to_pages() {  
    register_taxonomy_for_object_type('category', 'page');  
}
add_action( 'admin_init', 'wpse121285_add_category_to_pages' );

Add the appropriate category term to the desired page.

Then modify the default $wp_query object at pre_get_posts:

function wpse121285_pre_get_posts( $query ) {
    // Main query for the blog posts index
    // Note that you can use most/any contextual
    // conditional here, depending on your needs
    if ( is_home() && $query->is_main_query() ) {
        $query->set( 'posts_per_page', 5 );
        $query->set( 'category_name', 'news' );
        $query->set( 'post_type', array( 'post', 'page' ) );
    }
}
add_action( 'pre_get_posts', 'wpse121285_pre_get_posts' );

Leave the default Loop markup alone:

// No query_posts() needed here!
if ( have_posts() ) : while ( have_posts() ) : the_post();