Como dizer "De onde você a conhece?" em inglês

Surprisingly, it is also possible to say "to know from".

Where do you know her from?
I know her from the place where I used to work. (I met her where I used to work.)
I know her from college. (I met her in college.)
I know her from the gym. (I met her at the gym.)

As an alternative, you can also say "I used to know her at..." The inference is that you no longer have contact with her, do not know her well, etc.