Jester-bat

I'm thinking after that debacle with Joker Jr. and the death of Joker, Harley Quinn needed some help (partially because that nasty fall left her in no condition to actively continue her role for a while). So, she took a page from her late-boyfriend's book and "employed" someone from the Bat-Family to pick up the slack. In addition to being a fill-in, this would give Harleen a chance to assess herself, watching the subsitute-jester do whatever it is a Harley without a Joker is supposed to do.

Needless to say, Batgirl got the job done, making Harley both proud and mortified.