The majority of shape-shifters under Aku’s command do have human names. Some prefer to keep them, while others prefer to take names based off of certain characteristics (it’s their way of ‘starting fresh’ with no human ties). Snow, for example, was once known as Octavian Graucus-Pruina. It’s an old name… and a name he prefers to forget. Centuries in age, Snow no longer associates that name with his current life.
Flamey, not surprisingly, has a human name as well. However, unlike older shape-shifters such as Snow, she does not wish to forget it. She took her nickname in the hopes that Aku would not target her family… and so that other shape-shifters would not stalk her human roots. Wisely, she only shares her name with those whom she trusts. If it wasn’t obvious from her tipped nose, freckles, and russet hair, her last name is Celtic in origin: Kat Laisrén (which translates roughly into “flare” or “fire”).