New to WordPress, need help deciding tools for responsive development

I’m a web developer helping a friend out with her small business website she created in WordPress. She has the premium plan and is using the Appleton theme with Jetpack.

I’m trying to make sections responsive, but there’s no UI to apply different styles for Mobile (avoiding manual CSS, because it’ll be more difficult to teach her). My understanding is that I’d need to upgrade to business to use plugins like [Colibri WP](https://wordpress.org/themes/colibri-wp/) \- would that get me a more intuitive page builder that supports responsiveness.

I have others questions (should I be using [wordpress.org](https://wordpress.org) instead? Would she need to just pay to have that hosted?) but I don’t want to go too far into the weeds in my initial post here.

Thanks in advance!