My husband — a pastor/theologian — just made a list for my 14yo daughter’s high school years, so I’ll share a few of those.
On Guard for Students: A Thinker’s Guide to the Christian Faith, by William Lane Craig
The Case for Christ, by Lee Strobel
The Reason for God, by Tim Keller
Basic Christianity, by John Stott
Mere Christianity, by C. S. Lewis
Knowing God, by J. I. Packer
Can Science Explain Everything? by John Lennox
And I agree with CrystalN, that nothing will be more valuable than reading the Bible itself, along with some commentaries to help understand it. Here are some resources:
How to Read the Bible for All Its Worth, by Gordon Fee and Douglas Stuart – I consider this a must-read for new Bible students.
How to Read the Bible Book by Book, also by Fee and Stuart (book-specific background commentary)
Here’s a book that my husband also chose for my kids, but we haven’t uses it yet (there’s also a video teaching series): We’re big fans of the author:
https://www.ligonier.org/store/choosing-my-religion-paperback/
Here’s a website with excellent short videos on Biblical themes and topics. So enjoyable to watch!
https://bibleproject.com/
I hope that helps, and best wishes as you embark on this exciting journey with your daughter!