You are correct. She is neurotic. It has nothing to do with the teaching of the Catholic Church, even if she is able to quote snippets from Saint Paul and other Scripture, and from Catholic sources that “justify” her neurotic fear. That’s just the neurosis talking.
True, the Catholic Church does NOT teach that “once saved, always saved.” The Catholic Church teaches that it is POSSIBLE to commit mortal (deadly) sin.
But the Catholic Church DOES teach the mercy of God, the forgiveness of sins, etc. It’s right there in the Apostles Creed: I believe in the the Holy Spirit, the holy catholic church, the communion of saints, the forgiveness of sins, the resurrection of the body, and life everlasting.
Thx much AM. Very helpful.