I think it’s her colour. You see more white women with BME/mixed race guys than the other way round.
Don’t have any figures for the U.K. but according to the 2010 U.S. Census -
In 70% of marriages between African-Americans and European-Americans, it is the the husband who is African-American.
In 71% of marriages between Asian-Americans and European-Americans, the husband is European-American.
In 81% of marriages between African-Americans and Asian-Americans, the husband is African-American.