Dayna Mellanby was born on Earth but left as a baby with her father, Hal Mellanby after her mother, Karine Mellanby died supposedly in a Federation attack on their resistance group. This was about twenty years before her first appearance. When she first met Avon she described her education as having been by computer tutorial, but Hal somehow arranged for tutors to visit Sarran to advance Dayna's education, one of these being Justin whom she later visited on Bucol-2.
Known relatives: Hal Mellanby, father was killed by Servalan on Sarran. Karine Mellanby, mother was supposedly killed some twenty years earlier on Earth. Karine was a Federation agent who seduced and married Hal Mellanby. Pretending to be one of the rebels who surrendered and were then massacred by the security forces. However she was killed on Appallon Five by Kramer.
Dayna's adopted sister Lauren, a Sarran by birth, was captured by Chel and subsequently found dead.
Bodycount: Dayna claimed that she preferred "the ancient weapons - the spear, the sword, the knife", but showed no aversion to using modern firepower. In Aftermath she shot two Sarrans dead with a bow, and claimed a fair few more kills thereafter: Klegg in Powerplay; Mori and a trooper on Obsidian; two of Bayban's men with a heat-seeking bomb; two troopers in Rumours of Death; the General in Traitor (in a hand-to-hand struggle); two of Justin's creations on Bucol-2; four troopers in Games (3 shot, one with a Mecronian throwing knife); shot a guard on Zerok and killed up to three more with a grenade. She failed to outshoot Arlen on Gauda Prime and was shot, presumably fatally.
From Volcano Significant brawls: She overpowered Klegg in Powerplay; wrestled with Jarvik on Kairos; failed to restrain Bayban in City at the Edge of the World; knocked out one of Sula's rebels in Rumours of Death; fought menials on Ultraworld; needed the help of Kate and Pella to defeat Gunn-Sar in Power; and beat the General to death in Traitor.
In Dawn of the Gods Captured by: Klegg's troopers in Powerplay, Mori's men in Volcano, the Caliph in Dawn of the Gods, Servalan in The Harvest of Kairos, the Ultra in Ultraworld, Grose and Lector in Moloch, Servalan again in Terminal, trapped with Dorian's creature in Rescue, captured by Hommiks in Powerplay and used by Pella as a hostage in the same episode. She was later caught by the space rats in Stardrive, Servalan in Animals (where she was conditioned to first hate and then love Justin), and by Belkov in Games.
Rescues: Dayna's first appearance was when she rescued Avon from the Sarrans in Aftermath. She later helped Avon rescue Servalan from Chel's camp. In Ultraworld she saved Tarrant from the Ultra and later with Tarrant rescued Avon and Cally moments before they were fed to the Core.
Significant injuries: Dayna was in fact very rarely injured. She was hurt but evidently not seriously when Bayban escaped from her in City at the Edge of the World; thrown off a cliff by Og in Animals, found unconscious by Servalan's mutoids and tortured by Servalan; knocked unconscious by Muller's android; shot in the arm by Reeve in Sand, whereupon Tarrant insisted she return to Scorpio; and suffered what appeared to be a fatal shot from Arlen in Blake.
Places visited: She was seen to set foot on Sarran, Obsidian, Crandor, Kairos, Keezarn, Auron, Earth, Ultraworld, Sardos, UP-Death-Watch, Terminal, Xenon, Helotrix, Caspar, Bucol-2, Domo, Mecron II, Virn, Zerok, Beta-5 and Gauda Prime, a total of 21 planets.
The weapons she designed made occasional appearances. A green handgun in her bedroom locker on Sarran was used by Servalan to kill Hal Mellanby and later fired by Chel in Aftermath. It was seen again (probably a different weapon of the same design) with Cally in City at the Edge of the World, where it was said to have a killing range of "only 200" (presumably metres, since other metric measurements were stated in the episode). It was also given by Servalan to Deral in Children of Auron. Another of her inventions was used by Tarrant to vaporise the android Vinni in Death-Watch. A heat-seeking grenade that moved along the ground killed two of Bayban's men in City at the Edge of the World and distracted the Ultra from Tarrant in Ultraworld. In the same episode she blew an escape route for herself and Tarrant with micro-grenades concealed in her mouth.
She was seen to fire the Liberator's main armament just once, in Dawn of the Gods. In Headhunter she was seen supervising the medical treatment of Vila and Tarrant.
She gave Avon a single kiss on the lips in Aftermath and told him he was "very beautiful". This was when he was recovering and lying down. The kiss was not reciprocated by Avon and could be put down to her being very spontaneous and also having being isolated with just her father and sister for company, so not being used to social norms. Her only other romantic moments were with Tarrant (for the benefit of the Ultra), and with Justin, whom she was induced to first hate and then love by Servalan. She appeared to recover from his death fairly quickly, though.
Despite her avowed intention to kill Servalan, she never managed to do so and in fact rarely tried, though they met in a number of episodes after Servalan killed Hal: The Harvest of Kairos, Death Watch (where she resisted killing her on Avon's express command), Terminal, Traitor, Animals, Assassin, where she was taking aim when the gun was kicked out of her hand by Benos, and finally on Beta-5 in Gold, where she took no action against her.
Her relationships with the rest of the crew were obscure, except in the case of Vila where she was openly contemptuous on a number of occasions. She made no further advances towards Avon and none towards Tarrant. She did, however, seem tied to the crew by more than the simple desire to kill Servalan. Her initial enthusiasm for killing in general seemed to abate fairly rapidly after boarding Liberator. She regarded Justin's work with undisguised revulsion at first, and expressed a general distaste for war in general.
In Sarcophagus she was seen with an electronic lyre-like instrument, but her interest in music appeared to be no more than a passing whim at this time.