I don't know if Americans prefer Tess. I do myself.I've actually known both a Tess and a Tessa. Neither is Catholic. I don't know about either of them if their names are really Theresa or if Tess and Tessa are the full names.
I've never known a Catholic Tessa - just Theresas, including one Theresa who might not be RC - I've never asked her. Tessa seems to have peaked here in the 1940s-50s.