[watcher101]

From what I understood, when Aisha went to the past, she ended up in her great aunt's era, as implied (even stated that her aunt had the same name as the wise woman and that they looked identical when she was a child). Aisha was from this time period, but her parents went missing while searching for Auric's tiki.
Aisha stayed in the past and Tanya went to the future, but when time reverted to normal, Tanya aged with it, and thus missed out on her childhood.
When Tanya got the letter from Aisha (whom I'm guessing was an old woman at this point), she was give the location of where her parents were from the wise woman (whom I assume was long since dead at this point and Aisha held onto the information until the time where Tanya arrived in the future came).
The magic island Tanya's parents were on, it seems, existed outside of normal space and time, and thus her parents didn't age while on it, or time simply moved slower there.