Mireille is Roman Catholic, and her adopted patron saint is Saint Rita, the "Saint for the Impossible". Mireille's paternal grandmother Germaine née Charreton, assured her that Saint Rita was the one to intercede to God for hopeless cases. Beyond religion, like many artists, she is unabashed about superstition and luck. When asked to reveal some of her superstitions, she said: "The most important one is to never mention any of them." She has stage fright, and can often be seen making the sign of the cross before moving out on stage.