Sibling Rivalry

I don't know if it is the age difference or just normal sibling stuff but the girls have been fighting a lot with one another. And this morning it ended with blood. I was so happy laying in bed, Hayley was sleeping all peacefully and I was excited to get some sleep. Cassidy is sick and so she was staying home so there was no need for me to get up and rush around, I was excited. And then I heard the girls in Cassidy's room. Obviously they were up. I heard them bickering and heard slapping noises and as I was on my way down the hall to stop the fighting, I heard a huge thud like sound, almost like a piece of furniture falling or something, it didn't sound like it could be human. I walked faster and when I got into the room I see Kendall bent over laying on the floor, doing the silent cry. Next came the loud scream and crying. I asked Cassidy what happened and of course, in her eyes, nothing at all happened. I picked Kendall up and that's when I saw the blood gushing out of her nose. So, this time I asked Cassidy what happened and I asked more sternly (that's putting it nicely, lol). She said she hit Kendall and threw her off the bed!!!! I brought Kendall into the bathroom to check her out and the blood wouldn't stop. So, I called my mom to ask what a broken nose looks like because I had never seen one and there was a lot of blood. As I was talking to her, Kendall informed me she was "all better mommy" so I knew it wasn't broken, lol. I cant believe Cassidy did that, is fighting that bad normal? They haven't played with one another since, lol. Not because they dont want to but I have decided not to let them today. Plus, Cassidy is sick and I don't want Kendall or Hayley getting it so Cass is in her room with the mini dvd player. She is pretty content being in her own world today, lol.