My mom highlighted my hair a light brownish color and I didn't like it so I tried to dye it back to black, but now it looks horrible! How do I get rid of the black hair dye and make my hair lighter in a few days? I need to fast! IT LOOKS REALLY BAD!

There's a shampoo that strips your hair of deposit color. You should hope that you used semi permanent! :)
The shampoo is called "sunday shampoo" by bumble & bumble. You can only use it once a week because it is so strong.
I would suggest any clarifying shampoo that would fade out the color. Ask a stylist at a salon.