Gemma "Gem" Seddon is the aunt of Lewis and the mother of Jed Seddon.
In Series 2, she opens a burger van with her son and nephew outside the school at break and lunch times to make some quick cash off the students' unhealthy eating habits after junk food is banned in the school. Jed also sells drugs out of the van with the help of Lewis.
Gemma and Jed later show Lewis their drug factory shed full of MDMA-making equipment. After Jed beats up Lewis for spiking Chlo Grainger with their MDMA and threatening to call the police if Jed touches him, Lewis goes straight to Jack Rimmer's office and informs him and Andrew Treneman of the drug factory's location. When Jack and Andrew find it, they call the police and Gemma is arrested, though Jed avoids arrest and later turns up at the school after dark, where he fights Jack and accidentally fatally stabs Izzie Redpath, before sprinting away.
Neither Gemma or Jed are seen again.