Fixing a URL call from plugin

I host my blog within a directory (/blog) most plugins are able to cope with this, but occasionally one will not. I am using Donate Plus and once a donation has been completed, the button directing the user back to my site calls the url which is incorrect as it calls https://farmvillefanatic.com/blog/?thankyou=true when I need it to call https://farmvillefanatic.com/?thankyou=true

Here is the code that is causing the issue I believe:

$button = $img_urlz[$dplus['button_img']];
			if( $dplus['wall_url'] == 'sidebar') $wall = get_option('siteurl');
			else $wall = get_permalink($dplus['wall_url']);
			if( strpos($wall, '?') === false )
				$tyurl = $wall.'?thankyou=true';
			else
				$tyurl = $wall.'&thankyou=true';

How can I change this to correctly call https://farmvillefanatic.com/?thankyou=true ?

Thanks!