Found evidence on OUR site ... she is commemorated April 9
The mother church of Boscastle is Minster, dedicated to Materiana, and nestling among the trees of Minster Wood in the valley of the River Valency half-a-mile east of Boscastle. The Celtic name of Minster was Talkarn but it was renamed Minster in Anglo-Saxon times because of a monastery on the site. Until the Anglican Reformation of 1752, Materiana's tomb was preserved in this church. Traditions of the saint were recorded by William Worcestre in 1478 who states that her tomb was venerated at Minster and her feast day was [[April 9]].