She is the ACAM (Alignmented Christmas Angel of Mars) who was put inside Viking 1 by a kid and sent to Mars. She is known to have a strong love for Christmas, as she is a Christmas ornament and has been mentioned many times that she's never seen the top of a Christmas tree.
Tinselina knows quite a lot about the Wonder Luxe Appliances' dislike for humans and how they escaped to Mars to last forever. She even assists Toaster when he and the Supreme Commander compete for the Supreme Commander title in order to save Robbie (the Little Master).
After the election, Toaster and his companions rescue the Little Master and then invite Tinselina to come back to Earth with them, to which she happily accepts. She says her goodbyes to Viking 1 and departs, but their launch is halted when Toaster and the ex-Supreme Commander have to jump off to stop the Missile from destroying Earth.
They succeed in deactivating the rocket, and since it looked like they would be trapped on Mars forever, Tinselina insists they go back for them, but the Microwave points out that they don't have anything organic to zap them into hyperspace. So after rescuing Toaster and the Hearing Aid's twin brother, Tinselina gives up her hair and dress, since what she has on her is organic, and they return safely home.
After landing, Tinselina sadly throws herself into the trash until she is later found by Robbie. The Master (Rob) and Chris then give her new hair, a new dress, and place her on top of their Christmas tree, thus fulfilling her wish.