Answer: twinsister

AnswerCrossword Clue
TWINSISTER

Ann Landers or Abigail Van Buren

TWINSISTER

She may be fraternal

TWINSISTER

Ann Landers, to Abigail Van Buren

TWINSISTER
"Identical" sibling
TWINSISTER
Landers' Abby, e.g.
TWINSISTERFraternal one, perhaps