Does my sister have a disease or something?

She screams way too much and she is 12 years old. She was also born premature. For example, every time my dad says my sister can't go outside, she screams and starts wining like a 4-year-old. Another time recently is when I took off the brakes on my sister's Tango (a three-wheeled scooter), she screamed at me. I can't see a problem with that. And even when I tell her they don't work, every time her excuse is "I don't care". Also, my sister is very, very annoying. She doesn't care about any one and just her self. She sings loud and she's a bad singer and my mom always tells her to shut up and go into her room and sing but she just goes right ahead and sing again. There is a bunch of other stuff that stresses both me and my family out but there is not enough room to discuss it. Is this a disease and if so what is it named? Also, can it be dealt with by a therapist? Someone who knows anything help me!

Sounds like a combination of hormones and what I like to call "spoiled little princess" syndrome.

It kind-of sounds like ADD symptoms, do some research and see if her symptoms match.... it's either that or she is just spoiled.

she is definately just a brat.

She's a spoiled brat with add. Beat her up everytime she screams.