This web site, first of all, has a lot of great resources. I would also suggest the “Compendium to the Catechism of the Catholic Church” (a much thinner book than the actual Catechism).
The girl and her “Bible-only church” are following their interpretation of the Bible. And as for where they got that Bible from… the Catholic Church! The Church continued its existence outside of what was written in Scripture, and continued after the last word of what would later be called “Scripture” was written. If they looked at how the first and second century Church worshiped, and what they believed about the bishop of Rome and the Eucharist, they might be surprised!
The Bible – or at least, the New Testament – was not written as a guide for how to do Sunday worship, but rather as a testimony of the early Church. What was accepted as the “canon” of Scripture was those books which were allowed to be read during the worship of the Church (that is, at Mass). Simply because Scripture doesn’t record a particular practice or event does not mean the practice or event didn’t happen or isn’t apostolic.