Who the hell knows. The whole thing is so saturated with lies and misdirection and myth that the truth is very hard to discern. And why would Susan Blake have known the mysterious Anna 0bama anyway.
The same reason as there is a group of 'classmates' who can't show you an entire page, let alone a YEAR BOOK from Mercer Island High School...for the period that Stanley Ann Dunham was supposedly enrolled there.
They are the same group who 'visited Stanley Ann Dunham at the Seattle address' FOR ANNA OBAMA.