Come on, Tanya knows her past and she knew her parents, they are the religious fuckers that threw her out for getting pregnant. So, no. Also, Tanya is the same age as the MC, when Melissa (the sister) is Cat's age. Again, no.
Time travel, now? Oh boy, you may need to go take 3 or 4 cold showers in a row, to calm that fever. ::SMH::
While I sure do want the return of Melissa (Yeah I am one of the weirdos that don't think she's really dead) I don't want or need complicated hypothesis or over the top conspiracies. I also don't subscribe to the idea that she is already in Gilford.
After all, when Nana has sex with the MC, there's a LOAD of updates to fill with content... plenty of time to search, find and bring home Melissa. If it will please the Dev, obviously.
Peace