Grapher Having Problems After High Sierra Upgrade

My wife just upgraded to OS 10.12.6. She uses Grapher to make pictures for work. Now Grapher can no longer read her old .gcx files. She had a template she was using a lot. So, she had to remake the template in the new Grapher. It worked at first, but now Grapher won't even open that file. Has anyone had this happen? Is there a potential fix? I tried to Google, but no one seems to care about Grapher.