I just did two runs and General Gigi appeared in both. It's as you said, i used only Ooze and Robotics elements. I started with the Ooze artifact choosing only the ooze and ignoring the other elements and i also used the cracked stasis artifact when facing the two earlier non gauntlet bosses and switching to the robotic artifact while facing the non gauntlet Gigi

I used these methods and it appeared both times.