We have a C of E baptism for James born 1850. There's an RC one too. This says that Samuel was a Protestant, therefore Margaret was already RC:-

Event Type: Christening
Event Date: 20 Oct 1850
Event Place: Douglas, Isle of Man
Father's Name: Samuel Stewart (Protest)
Mother's Name: Margaret Wright
God Parents: William Maxwell & Mary Wright

Link: familysearch.org/ark:/61903/1:1:XZ1K-SXG