Although it’s possible to wield 2 rings/colors at the same time, there’s no known instance where the rings were merged.
From – Harley’s Little Black Book #2
You missed
%d
HOLY SHIT…if there was a lantern corps based on Malice/ill-will, This weird demonic Harley would certaintly become part of it. I can just imagine the damn scene: <>
Other than the black in her uniform there is no evidence of a black ring, she never puts one on, never uses one and there is zero mention of one…. zero credibility to this article
You sure about that pal?
http://dc.wikia.com/wiki/Harley%27s_Little_Black_Book_Vol_1_2
A Red Lantern Ring merges with a Black Lantern Ring and posesses Harley. Hal Jordan must prevent her from wreaking terrible destruction.
http://www.dccomics.com/comics/harley%E2%80%99s-little-black-book-2015/harley%E2%80%99s-little-black-book-2
Guest-starring Green Lantern! Black and red are kind of Harley Quinn’s thing…so when the most unique power ring in the universe crosses her path, she has no choice but to put it on, right? Unfortunately for Harley—and everyone else—this hybrid ring is fueled by rage and death…and things are gonna get out of hand very quickly!