She may have been part of the overlap on time between pre-congregation and 'post-'congregation.
From
Wiki, Pre-congregational saint is a term for a saint whose beatification and/or canonization occurred before the institution of the modern investigations performed by the Congregation for the Causes of Saints (i.e. pre-11th century). It designates those who were canonized by local bishops, primates, or patriachs, often as a result of a local custom, veneration or devotion.
The “pre=11th century” noted in the article isn’t exactly the right date. The Congregation for the Causes of Saints was created in 1588, parsing its function from the Congregation of Divine Worship. Formerly, the two congregations were known as Sacred Congregation for Rites.
It stands to reason that her death in 1224 in Brusthem near Liege, Belgium, happened while the Church was less…federated and without rapid communication with Rome. Most likely, St. Christina’s cause was taken up by local people and became a popular devotion. Around that era, any formal canonization would have been taken up by the local ordinary, such as the Bishop of Metz (7th - 11th Centuries) or perhaps the Bishopric of Liège.(13th century).
Per
this essay, “The earliest account of the life of St. Christina the Astonishing comes to us courtesy of the 13th century Dominican, Thomas de Cantimpré, who wrote the lives of several holy men and women from the diocese of Liége. The tales of Christina’s wild exploits might have been dismissed as an example of the medieval imagination run amok, were it not for the eyewitness account of Cardinal Jacques de Vitry, a man considered, then and now, to be a reliable and sober character.”
The best way to learn more about her and her life is through wriitings of her contemporaries. Allegeldy, she was noted by a Bishop and a Cardinal, but I do not have their names. She was invited to the above named convent by a friend named “
Beatrice,” who must have related her tale to someone (or wrote it herself) for us to know about Christina’s final days.
I’m also wondering if a lot of the medals sold aren’t confusing St. Christina of Bolsena, whose remains are buried in Palermo, Sicily, with Christina the Astonishing, whose remains are at Dominican Monastery of Saint Catherine in Saint-Truiden – in a similar way in which St. Teresa of Avila and St. Therese of Lisieux are often confused. Both Christinas share their feast day.
Have a look at the references on the Wiki page, and take time to ask blog authors to cite their sources so you can do a bit more digging. Best of luck!