I don't think that Katherine Kent was born RC. She became a Catholic in her middle years, and that meant that her husband would be out of the succession. However its hardly much of a sacrifice as he was so far down the line
Actually, there was a Quirk in the Act of Settlement and Katharine Kent's conversion did NOT take the Duke of Kent out of the line of succession as she converted after their marriage. It was marrying a Catholic that took people out of the succession.
https://en.wikipedia.org/wiki/Act_of_Settlement_1701
"Removal from the succession due to Catholicism
Since the Act's passing the most senior living member of the royal family to have married a Roman Catholic, and thereby to have been removed from the line of succession, is Prince Michael of Kent, who married Baroness Marie-Christine von Reibnitz in 1978; he was fifteenth in the line of succession at the time. He was restored to the line of succession in 2015 when the Succession to the Crown Act 2013 came into force, and became 34th in line.[18]
The next most senior living descendant of the Electress Sophia who had been ineligible to succeed on this ground is George Windsor, Earl of St Andrews, the elder son of Prince Edward, Duke of Kent, who married the Roman Catholic Sylvana Palma Tomaselli in 1988. His son, Lord Downpatrick, converted to Roman Catholicism in 2003 and is the most senior descendant of Sophia to be barred as a result of his religion. In 2008 his daughter, Lady Marina Windsor, also converted to Catholicism and was removed from the line of succession. More recently, Peter Phillips, the son of Anne, Princess Royal, and eleventh in line to the throne, married Autumn Kelly; Kelly had been brought up as a Roman Catholic, but she converted to Anglicanism prior to the wedding. Had she not done so, Phillips would have forfeited his place in the succession upon their marriage, only to have it restored in 2015.
Excluding those princesses who have married into Roman Catholic royal families, such as Marie of Edinburgh, Victoria Eugenie of Battenberg and Princess Beatrice of Edinburgh, one member of the Royal Family (that is, with the style of Royal Highness) has converted to Roman Catholicism since the passage of the Act:
the Duchess of Kent, wife of Prince Edward, Duke of Kent, who converted on 14 January 1994, but her husband did not lose his place in the succession because she was an Anglican at the time of their marriage."