Tempo's real name was revealed in X-Force (1st series) #26.
Originally, Tempo had the power to "make time fly with her", and her ability reportedly only altered the perception of time by living beings. It has evolved or been re-imagined to literally affect time.
Tempo was the only refugee at Fortress X killed during the seven real days of the Age of X. Mike Carey has stated repeatedly in interviews that this was meant to be a real death, even after reality reverted itself. Like many mutants, Tempo was resurrected on Krakoa, seen in X-Force (6th series) #9.