She is a supporting character of the Outsiders and a scientist responsible for giving Princess Tara/Terra and her elder brother Prince Brion/Geo-Force their earth-controlling powers.
In the Millennium storyline, written by Steve Englehart, Jace is revealed to be a villain with her own agenda.
Following a revolution in Markovia and the death of King Viktor, Jace gives Brion and Tara Markov powers to help them fight back.
[1] Subsequently, Jace becomes an ally of the Outsiders, during which she reunites Metamorpho with his lost love Sapphire Stagg and helps Halo regain her memories.
[4] In Doomsday Clock, Jace supports the Superman Theory, which states that some metahumans were created by the government.