The clerk in the bookstore is misinformed about the Church's position on Vassula Ryden, but this is understandable since Mrs. Ryden's website is full of pictures of her posing with then-Cardinal Joseph Ratzinger and other church officials as well as a long list of documents detailing her interaction with various church officials.
However, despite what is being promulgated by her organization, a ruling made against Mrs. Ryden by the Congregation for the Doctrine of the Faith in 1995 remains in effect:
"Given the negative effect of Vassula Ryden’s activities, despite some positive aspects, this Congregation requests the intervention of the Bishops so that their faithful may be suitably informed and that no opportunity may be provided in their Dioceses for the dissemination of her ideas. Lastly, the Congregation invites all the faithful not to regard Mrs. Vassula Ryden’s writings and speeches as supernatural and to preserve the purity of the faith that the Lord has entrusted to the Church."
For those who are not familiar with Ryden, she was born to Greek parents living in Egypt in 1942 and claims to be receiving messages from Jesus and Mary. A member of the Greek Orthodox Church, she has documented these messages in multiple volumes of a book entitled, True Life in God, which is riddled with New Age spirituality, millennialism and a false ecumenism. Even more problematic is that these messages were received through automatic writing, also known as trance-writing, which is a form of mediumship.
In 1995, the same year as the Vatican issued its notification about Ryden, Dominican theologian François-Marie Dermine, a Canadian-born priest serving as exorcist for the diocese of Bologna, Italy, wrote a book, Vassula Rydén: Critical Inquiry, in which he analyzed Ryden's work and found it lacking in many regards. A very informative document by Fr. Dermine about Ryden can be found here.
Essentially, Fr. Dermine cites Ryden for cancelling messages that she discovered to be false, saying that God told her she could change any messages that didn't work. He also cites theological errors and the "Vassula-centrism" of the messages for his opinion that Ryden's writings are not from God.
Ryden's website displays a letter allegedly written by then-Cardinal Joseph Ratzinger in 2004 saying that participation in her ecumenical prayer groups should be left up to diocesan bishops. However, Cardinal William Levada, prefect for the Congregation for the Doctrine of Faith confirmed as recently as 2007 that the 1995 notification against Ryden was still in effect.
In addition, the Greek Orthodox Church also condemned her teachintgs in 2011 and the Church of Cypress did the same in 2012.
TC, my recommendation is to return the book and please inform the clerk that the 1995 Notification against Ryden is still in effect.