She is a lot like her father, Loki. She takes deceit and lying very seriously though and she refuses to lie about stupid or petty things. If lying will benefit her, she will, and she'll lie so good she's rarely ever found out. However when she's not lying she's honest to the point of being brutally blunt.
She loves a good joke or prank, especially at the expense of others, but when the laughter is aimed at her she can be very hypocritical and does not take it well. She'll even go so far as to get revenge on people that laugh at her.
Her and her twin sister are born in 914 AD to Loki and Lagertha, a shieldmaiden. They were raised in true Viking style, and when they were old enough Gyda was eager to become a shieldmaiden just like her mother, though her sister <so and so> was less eager and was more interested in possibly being wife to a Jarl some day. Because Vikings actively believed in the gods and worshipped them, there was no need for secret training camps. At 19 I'm going to work out that something happens that causes them to be indebted to Odin, who turns them into Valkyries and owes them his service for 1000 years. However, something happens at some point that adds another 1000 years onto their service. Although recently, there has been some friction between the Norse gods and the Greek/Roman gods and he's going to strike a deal with them that if they do some things for him, major dangerous things, he may end their service early.