Gretta is the twin sister of a previous character, The Blacksmith. She was upset by her death and blames the Earps for it. To get revenge she makes a crooked deal with Waverly Earp to get the genie demon Marzaniok. She wishes for Wynonna Earp to disappear. The result is an alternate universe where Wynonna never even existed.
In this alternate universe, Gretta was even worse off than before. And her sister was still dead regardless. She worked on a reversal spell to temporarily bring back the memories of the real universe.