It seems to me that something was corrupted with your installation, as by default jquery.js should be located in the path set in your installation. At this point, I would backup your installation – be sure to do this – I claim no responsibility for lost anything, then if you are using WordPress 3.0+, log in to your dashboard, select Updates from the sidebar, and use the Re-install Automatically function.
Without jQuery, the following code will never run, as the browser has no idea what jQuery() is:
jQuery(document).ready(function(){
jQuery(navigationArrow("https://princess.zettai-glay.com/wp-content/themes/modularity-lite/images/arrow.png"));
jQuery(function() {
jQuery("#slideshow").cycle({
speed: '2500',
timeout: '500',
pause: 1
});
});
});