After prologue in TLOU, it cuts to Summer - 20 years later. Then TLOU campaign takes about a year until it's over.
TLOU 2 takes place 5 years after TLOU is finished.
It has been at least 25 years since pandemic started in TLOU Universe.
Or was she only made Transgender because Neil Druckmann loves taking advice from Anita Sarkeesian?
Abby still seems to have a physically masculine build from the images I've seen, so likely hormones haven't come into it.