I don’t know what you were doing in her diary, but you don’t have anything to do with that information but to tell your parents. You may owe her a big apology and she may never forgive you as long as she lives, BUT do not pass GO, do not collect $200, but go straight to them and tell them about this. No matter when it was, tell them. Suicidal ideation is something that adolescents throw around, but is it also a very serious mental health symptom. It cannot be ignored. Do not try to handle it yourself. Call help in.
If you want her to learn responsibility, you expect her to be responsible. When she tells you to go get something for her, you say, “no, there is no reason you cannot get it yourself.” Maybe she threatens that she won’t ever get anything for you, but let’s face it: on the balance, not a big loss to you. Let that one pass without comment. If she keeps threatening and does not move, just say, “well, I will have to live with that. I’m not getting your phone for you.” Then go do your own thing.
If she wants you to do something on the pretense that she does not know how, tell her, “well, it is time you learned. I will watch and give you lessons, but you’re doing it yourself.” If she abuses you as a teacher just once, you tell her this: “Listen. I am not your mother. It is not my job to teach you this. If you want me to teach you, then don’t be rude. The next time you’re rude and you ask me to show you how to do something, the lesson is over and you are on your own. Got that?” Then stick to your guns. If she wastes a whole batch of something “because you wouldn’t help her,” oh well. The alternative is letting her walk all over you. You are done with that.
On the count of “she hates my friends and she has no respect for me,” there is a a little shame on you in that. She probably does not actually hate your friends. She resents your friends, probably because your friends’ choices do not revolve around her. Don’t stick around to listen to her bad-mouth them. Do not stick around to listen to her badmouth you. Do not stick around and listen to her bad-mouth anybody. Is this what you take from your classmates? Do you just listen to the bullies putting other people down? Do those nasty people order you around and do you do whatever they say? Why do you take it from your 12-year-old sister? If she wants to hang around with you, she’s going to have to learn how to be polite. Otherwise, she’s going to have to start spending her life with no one to socialize with except authority figures–that is, parents and teachers.
It is a bit premature to expect her to be a strong woman. She’s 12, and she may be a late bloomer on top of that. Satisfy yourself with expecting her to be more self-sufficient (which will increase her self-confidence) and more civilized towards you, your parents, and your friends. That means you will have to restrain yourself from doing things for her and requiring her to do them for herself, even if it means teaching her. It also means insisting that she have some decent manners if she wants you to acknowledge what she says or does. Otherwise, treat her like a pre-verbal child. You can notice her, but ignore the substance of what she says if the substance of it is rude.
Mostly, though, make sure your parents are kept up on any disturbing behavior on her part. Do not make it pay by making a fuss over her about it. Suicidal talk is damaging to the speaker even when it is “meant” to upset the listener and not as a “real” threat. That kind of talk gets into one’s head. Find out from a school counselor how you ought to handle it, and do that. Expect to take the talk seriously but not to allow it to become a way that your sister manipulates you…but that will take a conversation that you ought to hear first-hand and in a setting where you can ask questions from a professional, OK?
Now I am going to tell you about a little experiment they have done with rodents. They gave these little mice or rats or whatever they were a little machine like a slot machine, and whenever the rodent hit a little bar, some little treat would slide out. So far, so good. Then they did experiments with not rewarding the rodent every time it hit the bar. They set the machines on reward-every-certain-number-of-tries (such as every fifth try), and on reward randomly (like a slot machine). After that, they turned all the machines off and tried to see how long it took to extinguish the behavior. The behavior of hitting the bar for a treat was considered “extinguished” when the little animals had finally given up on trying.
Now, just guess which setting resulted in rodents that took the longest to quit trying. I think you will have guessed right–the rodents with the machines on the “slot machine” setting took the longest to figure out that the machine had been turned off, followed by the ones that had an “every fifth try” machine, followed by the shortest time to extinguish the behavior, which was when something that used to ALWAYS work suddenly NEVER worked. And of course you can visualize what happened with the machines that used to deliver every time when they suddenly went off. Those little rodents hit those bars like crazy and every weird way they could think off before they were convinced that their treat machine was broken.
Do you get the picture? Decide ahead of time what you are going to do to “cut off the reward” for your sister, and be VERY consistent. EXPECT HER TO RAMP UP BY “HITTING THE BAR” LIKE CRAZY AND TRYING TO KICK THE SLOT MACHINE. Do not give in and let her manipulate you into doing what she wants any more. Instead, expect her to do what she ought to do, and only give her the kind of feedback she wants when she does what she ought to do. Otherwise, give her NOTHING. Not just no cooperation, but no drama about it. She likes drama, too.
First off, for the most part this sounds like a somewhat typical thing that kids going through puberty often go through. This is a very difficult age for your sister with hormones and other changes she is going through right now. It’s very common for parents to “baby” the youngest child in the family. What I would personally do, is number one pray for her! Pray for her often! I would ask for the intercession of St. Therese, or St. Rita. St. Dymphna is the patroness of those suffering with mental afflictions, and supposedly St. Kateri is also the patroness of suicide victims, and St. Maria Goretti is the patroness of teenagers. I don’t think you should go through her diary; privacy is very important to girls at this age. If you truly feel your sister is suicidal you probably call the National Suicide Prevention Lifeline. You can click on this link to learn more about them