The "Element" series always depict in their card backgrounds, the elements in which they gain their effects from. In this case FIRE (on the front of her weapon) and WATER (on the ground).
On the opposite side of her weapon, there appears to be steam coming off of it, and in the background, there are three volcanoes erupting.
Like all members of the Element series, "Element Valkyrie's" color scheme matches her attributes. In this case, she has a blue left eye and blue armor (WATER) as well as a right red eye, red hair, and red clothing (FIRE).
Due to the spelling of her name in Japanese, she isn't part of the "Valkyrie" archetype.