It used to be thought that Elizabeth Christian was Rev. Thomas Allen's wife. It has since been shown that she was his daughter, the wife of Edward Christian, Lewaigue, Maughold. The confusion probably arose by the use of the abbreviation "als." Nowadays we take that as the equivalent if née, but in the 17th century examples are found where it simply means "alias", the order of surnames not necessarily following the usual pattern.
Rev. Thomas Allen's wife was Kathren Fletcher, buried 1652, as you found.
Nigel Crowe posted about this on 11th June 2009.
Philip Allen, 9th great-grandson