Ah, Lady Blue! Now she's one I'd love to know more about myself... and how she pulls off those temporal shenanigans!
I've got a couple theories but nothing I can confirm yet! Although my guess is it really is that belt of her's, which uses some kind of undiscovered power source, ooor...
An agent from the Time Anomaly Removal Crew or Time Paradox Avoidance Enforcement Squadron in the far future was sent back to this period, and after encountering them she stole their time-travel device!

[From personal experience, he'd actually wager the latter is the more likely scenario.]