At the top of the apartment complex on the southern side of the south island awaits Sanchez. A quick way to reach her is to climb the windows of the blue, western building to reach the top. Thankfully, there are not too many armed guards at the top. She should not pose much of a threat. Due to the rooftop's close quarters, your melee attack can be quite useful. In addition, shoot explosive barrels if Sanchez is anywhere near them to damage her significantly.