Arrena is the natural daughter of Lord Jothos Harrigon and a peasant girl whose father temporarily worked for Lord Jothos. After her birth, Jothos took Arrena in to be raised in Smithestone's walls along side his true-born sons and daughters. Her mother and grandfather eventually left Smithestone, and they were never seen again, though they would write to Arrena from Oldtown every so often. When she came of age, Arrena was trained as a blacksmith, learning to forge swords and knives,
Arrena had been working in the forges of Smithestone for a number of years until her father married her to Ser Ethan Snow, the master-at-arms at Helgen in the North. This was part of an alliance with the Dragens, which also married Arrena's half-sister Larinna to Lucius Dragen, the new lord of Helgen.
She knew that Lucius was abusing Larinna for weeks after their marriage, but never attempted to stop the violence, as Lucius threatened her and Ethan if she tried.
Arrena soon gave birth to Merei, whom she and Ethan gave the name Whitesnow to in order to remove the trace of bastardry from her. Arrena was with her sister Larinna in her birthing chamber, the first time when she gave birth to Warron and a second time when she gave birth to Melina.
Arrena is made aware that Ethan Dragen, now the new lord of Helgen, is being pressured by House Dragen's vassals to divorce Arrena and marry a woman more suitable, as Arrena is still a bastard. Maester Vahaelor hears of this and fears that if this happens, House Harrigon would end their alliance with the Dragens. In a short amount of time, both Lord Ethan and Lord Rickard both agree to have Arrena legitimized.