Patrisha used to be very different from how she is now. She was born not quite the same. She was born a boy. Her entire life, until she was about 16 or so, she didn't like the way she was. No one would talk to her about her problems until one friend told her to believe in herself and make the change. So, with her father's money, lying and telling him it was for some sports team or something, she got the horomones and surgery she needed to become the beautiful woman she always wanted to be.
Eventually, she couldn't keep hiding it from her father and was found out, then promptly thrown out of the house. She was alone then, though she was 18 by this point and able to fend for herself, mostly. She decided that North America wasn't the place for her, so she went west, across the ocean. She found herself in Russia and hopping from town to town. Eventually she found a place to settle down for a few years and actually found a man for a while.
Eventually, he found out what she used to be and she was kicked out of that house. Deciding to make yet another new life, she went down to Chernarus just in time for the infection to break out. Stuck and hoping to survive, she did everything she could to survive, then eventually thrive, in the new world.