It is so strange of you. In order to get black eye look, you could do the eye make up to get this. It is very real at the look which you could have a try which will not have the damage on your eyes. You could use the eye shadow to do the black eyes look. You could also wear the sunglasses which could make you look more like owning the black eyes.
Well, generally speaking, black eye can be kind of normal in daily life. And in common, a black eye can occur, when blood and other fluids collect in the space around the eye. According to some researches, it is often caused by the injury to the face or the head. When black eye occurs, swelling and dark discoloration in the eyes can be visible. For your situation, I will suggest you try using ice to reduce the swelling caused by a black eye. Also, warm compress will also be effective for your black eyes, for they can make your blood flow smoothly. So you can just put a warm cloth on your eyes.
Apology. I was short about giving yourself a black eye. It's not like I haven't has bad an idea. But Caroline, giving yourself, getting some else to, is a bad idea. Any of the ideas given can have really serious and possibly deadly results. Watching your sister, as bad as that can be, beats being blinded or killed. What's wrong with going out(side?) with her? Is it taking you away from online time? Just a guess. Best answer is find ways to interest your sister in more time inside. Think compromise rather than a very risky idea that has a problem getting your parents to free you from sister-duty.