My sister is kind of weird

My sister acts really mean to me. I have a little sister who is 12 and she is really mean. She has really bad mood swings and goes from being friendly to like screaming at me in a matter of 2 seconds. My older sister who is 15 is the only one who can control her. I am 14 and so I am right in the middle and I cannot get her to stop having mood swings and being mean and I think she needs help because she is obviously angry about something and I want to go back to being friends like I used to be with her and the worst part is is that she is getting violent and I cant have her being violent because we also have a baby sister who will be 1 july 17th and I dont want her to be violent aroud the baby but our parents arent around much to stoph her

Two things going on here:

1. Your sister is getting used to having woman hormones. It takes long time to level out. That is probably the cause of the thirty second mood swings. She will outgrow this.

2. She is being pushed out of her role as the baby of the family. This is scary. She is used to getting a certain type of treatment and attention that you older girls don't get. Now she has to join the ranks and watch the baby get all the baby attention stolen from her.

She'll get used to it. The best thing you can do is just steer clear of her. Time will help.

my sister used to be exactly like this, and the only thing that helped me was to leave her alone, don't talk to her much and just let her grow out of it, believe me she will. When she begins to get violent tell her that she shouldn't be doing that around the baby and if she does then you will tell your mom and dad. Also talk to your parents about her behaviour and make sure they explain to your sister that when they are not around you and your older sister are in charge. If your parents aren't strict now then she won't know whats right or wrong.

WOW. I'm in the exact position, except my sister is 10 and my 15 year old, is a boy. I'm the mid child too. And she is friendly and then mean the next minute. Okay I have somethings to ask. Do you ever talk back to her when she's being mean? Because if you do, stop it. When she's in her mean mode and she's talking/yelling at you, ignore it and answer simply. She should get the point and back off if you just try not to talk to her when she's like that. Remember, being calm proves a point. That's what I always do.

Umm.. I'm really offended..
I'm 12 and I act like that... ><
The thing is I was sweet when I was 11 and now I act the same as your sister. I'm pretty sure we've all been like that, okay? Just try to be nice to her as much as possible. And trust me, she will have the mood swings, just don't take it personally enough for you to actually have to tell people on this forum.. >>
Good Luck
And give her mountain Dew, it calms me down, and she might get pissed off easier if she's tired..