what to choose between ruby and react?

my best friend and I have a former teacher who connects students with companies for their first paid internship. She manages everything by hand (payment of salaries, networking, sending invoices...), and on her free time, which takes her a lot of time. We would like to develop her a tool that manages the generation of invoices in PDF, which would allow associations to post job offers, students to register and choose an ad. It's a big project to do, but it would save her a lot of time.

We know how to program in JS, CSS, HTML and RUBY. I wanted to know if to create this tool I had to improve my skills in react or in ruby.on.rail. Which of these two solutions would be the most suitable for the development of a tool of this kind?

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