The person who would become Elven, like Prime, is just a child who fantasized about fantasy lands and related more to the medeival fantasy genre than modern day super heroes. Thus, when her powers emerged she fastened them into an elf-like figure. Like Prime she possesses super human strength, endurance and flight after summoning a protoplasm-like substance over herself to transform her new body. When her powers emerged she identified them with magic and thus they took on that appearance as she released blasts and other offenses.
She was discovered and persued by the government who wanted to use her as a means to trying to create others like her.