One caution - an AncestryDNA test is an autosomal DNA test, not a mitochondrial DNA test, so is not likely to be helpful toward establishing links to Mary Cushman. Your DNA is diluted substantially with each generation, so by the 6th to 8th generation back, there is rarely a detectable amount from any one specific ancestor. Your only hope is to prove a match to someone who has proved a link back to Mary.
A mitochondrial DNA test would go back far enough, if there are others with mtDNA results to verify it. You can get that from FamilyTree DNA, the Full Sequence mtDNA test.