Question about Miyu's timeline...

Episode 22 is sort of Miyu's origin story and it takes place during the Taisho era (1912-1926, i.e. in between Meiji and Hirohito). It shows Miyu's awakening as a Guardian.

The rest of the series takes place, presumably, in 1997, barring any continuity I may have missed or forgotten about with the 1989 OAV series. So what was Miyu doing all that time (approx. 60 years) between the Taisho Era and the Heisei Era? Is there an episode that explains it?

Spoilers are welcome.

Thanks.