So your description is a black girl with big tits. How is that narrowing down anything?
Optimistic puts it lightly. It might well likely just be a normal civvy girl or one looking for a sugar daddy.
If you have any hope in hell locating this random person which is unlikely you need to be very more descriptive that you are.
Rough age estimate, complexion (I.e. caramel), height, build. Location you saw her, any noticeable tattoos/piercings. Basic information essentially, good luck with your search