Well, Forbes has offered an update on their previous report and in the update that say that Harley Quinn is, in fact, expected to be in The Suicide Squad. She is part of the most recent draft of the script. They also report that the movie will start shooting sooner than expected:
"I have learned from sources close to production that in fact, the information about Harley Quinn being absent from the new Suicide Squad movie is no longer up to date -- she is indeed expected to appear in James Gunn's The Suicide Squad, which is expected to begin production later this year."
What isn’t made clear