Scarlet Snow was the name a particular redcap gave to Maya Henderson for the purposes of bargaining with her.

He provided her with a tome that contained advanced rituals for Time magic in exchange for two parts of her True Name. She then used that ritual to pass back in time, and due to causality paradoxes (also known as timey-wimey bullshit), she arranged things so that she never gave him her True Name in the first place but kept her copy of the tome.