Rss to Email: Add Category title

Hi,
I’m wondering if I can add the Category title for each post in the e-mail newsletter. In my feed-rss2-php file I have the function <?php the_category_rss() ?> within <item> tag but it doesn’t show. Would I have to add some code to functions.php? I’d like to have a category header above each post, check it out: https://www.screencast.com/users/JuriT/folders/Jing/media/61d8f610-6cda-4a94-baba-8a97c16d2ad4

Thanks