While I have been unable to confirm this marriage I have no doubt that it must have occurred as her brother Captain James Cook refers to her in this way in his Last Will & Testament dated 14th June 1776 prior to his departure on his third and last voyage 25th June 1776 - Proved at London the 24th day of January, 1780
"I give to each of my sisters Christiana Cocker and Margaret Fleck the sum or legacy of Ten Pounds"
