How can I learn more about the Holy Spirit?

My girlfriend on Easter was diagnosed with stage 4 colon and liver cancer and by just the grace of God much of the cancer is gone. Since she grew up with no religion, I have been talking to her and doing my best with all the help coming from the Holy Spirit since I am not that educated on many avenues of my Catholic faith. All the glory goes to God for what she and I have learned but now she is asking me about The Holy Spirit and want to snail mail and email her the best material about learning about the Holy Spirit.
Will you suggest some?
She so is in love with the Lord now and has no fear of dying, just wanting to make it to Heaven by the grace of God.

Thanks.

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