If I had to hit the high points of each in such a short time, I would tackle it thusly, fleshing it out with Scripture and examples as appropriate:
The teaching is found nowhere in scripture. If something is so key to being a Christian, it should be very explicitly taught.
The very concept was virtually unheard of for the first 1500 years of the Church’s existence. It was not even possible for the majority of Christians to even dream of it before the invention of the printing press. Very poor planning on our Lord’s part!
It has proven itself impractible, since we have 30,000 different competing Protestant denominations who all claim to follow the Bible.
Point out that all the Church’s dogmas and doctrines about Mary say more about Jesus than they do about her. For example, her title of Mother of God safeguards the fact that Jesus is fully God and fully man.
When Catholic’s are accused of elevating Mary above Christ, they are presuming to read people’s hearts and minds. We do not worship Mary, but we give her honor because God has honored her.
The Scriptures attest to it, and the Early Church, and virtually all Christians until the Reformation believed in the Real Presence of Christ in the Eucharist.
Walk them through the Scriptural accounts of John 6, the last supper, and the Road to Emmaus stories.
I’d finish up by recommending follow-up resources. For high schoolers, the Beginning Apologetics books would be very appropriate. I’m sure you can think of more.
Good luck. Make sure you prepare with study and prayer, and let us know when the date draws near so we can pray for you too.