I think this is your most BRILLIANT cutie mark idea. It's time related for Time Lords, and it's a very complicated time device. That's the Rani in a nut shell. In her three appearances (including the 30th anniversary) Her schemes were more ridiculously complicated than the Master's or the Monks. It's so perfect, that you're a genius!
well considering she was a timelord, and the doctor had to (supposedly) kill off all the timelords, I'd deduce that she got the short end of the stick, along with poor Romana, but here's hoping otherwise!