Elaine Cassidy (Rosaleen O'Donnell) and Kíla Lord Cassidy (Anna O'Donnell) are mother and daughter in real life.
There's an example of postmortem photography in the O'Donnell's household. Photos were expensive during the set time period and usually only a wedding photographer was only ever employed, to take a picture of the married couple. But if a family member died, they would prop up the deceased and have a group photo taken so as to remember that person.
The song "Céad míle fáilte romhat, a Íosa" sung by the family is a traditional Irish language hymn that translates as "A hundred thousand welcomes, O Jesus."
One of the saints Anna discusses with Lib is St. Catherine of Siena. She was known for her extreme fasting, which was believed to have hastened her death. She is the patroness of those ridiculed for their faith and of nurses.
This film reunites Florence Pugh with her Lady Macbeth (2016) scribe Alice Birch. In the years since Lady Macbeth's release, Birch has become a very hot screenwriter and show-runner, and Pugh has become an Oscar-nominated actor.