The analytics script should be installed in the React theme. We plan to release a Google Analytics extension so you will only have to configure it with your GA ID. But the plugin you are using right now will not work anymore, with Frontity your WordPress becomes the source of data for your site (like a headless CMS) and the frontend is totally decoupled from the backend.
Feel free to take a look at the 1.0 roadmap where we announce the extensions that will be ready: https://community.frontity.org/t/1-0-roadmap-progress/207.