Do you mean that she screams with a sound from her throat but not while trying to say words? In other words, she doesn't talk? The screaming is not an attempt to talk. If so, I recommend that you get an evaluation for speech and development issues. She may have a sensory processing disorder as well as a speech delay which is causing her to scream in frustration. You can do this thru the school district without cost.
Even if her screaming is just that it's a bad habit, I would still have her screened. Something sounds amiss.
Does she point to things that she wants? Is she interested in playing with a variety of toys? Can you predict when she'll scream and note what is happening that might be frustrating?
If it's a habit left over from having discovered that she can scream you can influence her to not scream by not paying any attention to her when she's screaming. She will eventually learn that screaming doesn't work.
Is her screaming done in anger because you have said no? Then learning ways of directing her without the frequent use of no may help. Is your house child proofed so that there is lots for her to explore without having you have to say no?
As to her going ahead and doing something after you said no, this is very normal She is just beginning to learn about boundaries. You have to follow thru. I recommend distracting her by focusing her attention on something else. For example: she wants to play with the TV controls. You pick her up and put her in another part of the room away from the TV and hand her a toy she can play with. In this way she will eventually learn how to change directions for herself. This is a years long process.
I highly recommend reading a parenting book or two. 1-2-3 Magic is a good one. My favorite is Love and Logic by Foster and Cline.