Scavenger Alliance — Janet Edwards

Humanity has gone to the stars, but the rebels and the criminals were left behind. So were those guilty of nothing but being their children.

In the year 2408, eighteen-year-old Blaze is one of the last seven hundred people scavenging a living in abandoned New York. A century after the invention of interstellar portals, the respectable citizens have left for settlements in the countryside, or joined the great exodus of humanity to new, unpolluted colony worlds. Those remaining in New York are the undesirables that neither the citizen settlements nor the new colony worlds will accept.
 
Blaze's mother died six years ago. She believes her father is Donnell,the leader of the uneasy alliance between the remnants of the Earth Resistance and the old criminal gangs. It's less clear what Donnell believes, since he barely speaks to her. The alliance is crumbling under the strain of its hardest winter ever, when an old enemy tries to use Blaze as a pawn in a power bid. She thinks her life can't possibly get more difficult, but then an aircraft carrying three off-worlders arrives in New York.
 
Scavenger Alliance is set several centuries earlier than the Earth Girl trilogy, and features one of the ancestors of its main character,Jarra.