Quoting Lil Pumpkin in the Oven!:" My DD is 2 and whens shes mad or doesn't like something she will scream at the top of her lungs over ... [snip!] ... or her brother walking towards her with a toy or something along those lines its driving me insane idk how to get her to stop!"
When she does it pick her up and put her straight in her cot and walk away. Dont say anything and when she stops screeming go in and get her and tell her screeming is not okay. Keep doing it until she gets the point that your not going to listen to her do it