Updating PHP Sessions with a WordPress Form

I’m building a site for my Mother with a form to customize a doll’s name in the text on all pages. Since I want to do this on many pages, I’m sure that I need to use a session and have placed the code I found in the functions.php file of my Graphene child theme and call the variable into the post with the Shortcode Exec PHP plugin. However, when I enter a name in the form at the top of the Home page, nothing changes in the slider/post text (e.g. “‘s” should become “Name’s”, “Linda’s”, etc).

Any help would be greatly appreciated…