Header.php has disappeared from Editor

I am helping a friend and a few days ago she had malware on her site. Her host was able to tell us where it was located. It was in the Header.php file so I removed it and all was well. For 2 or 3 days. Now her header is gone and her entire page is enlarged, no menu. I went in to look at the Header.php again and it has disappeared. Now what? How do we add it back to the Editor?

Here is the link to the site: http://centsablecouponlady.com/

Thanks!