OK. Now that some of the riff-raff have been exterminated from this thread, let's see if I can shed some light on this by answering my own questions. You might be surprised by some of the answers.
And for full disclosure: I am a therapist who works primarily with teenagers and have been for 22+ years. I work with very difficult teens... difficult in the sense of depressed/suicidal. I have dealt with, probably, well over 100 suicide attempts... either from clients that I got AFTER their attempt, or clients who attempted while in treatment with me. In fact, on Monday of this week, I hospitalized a 17 year old girl for a pretty serious suicide attempt.
Also, I wrote my final paper in graduate school on Suicidality.
1) What person is responsible for the suicide?
The person who committed suicide. I know, some of you may be surprised by this answer, but you must keep reading to understand the rationale. We are each responsible for our behaviors and how we chose to respond to our feelings... the FEELINGS are what is beyond our control. Example: if I could choose how I feel, I'd be happy all the time. Now, there is a sequence of events that occurs in situations like what happened to this girl: triggering event ---> interpretation/thoughts/feelings of that event ---> behavioral reaction to that event. The same event can happen to several different people, and each of those people will interpret the event differently... because of their life experiences, state of mind, or something else. This girl was bullied. Many people are. How someone takes that bullying is an individual response which leads to an individual act. This is why the act of suicide is the responsibility of the individual who commits suicide.
Does the bully have any fault in this issue? For bullying, for sure. For contributing, for sure... however, there many be many other issues that also contributed. The bully is not to blame for the suicide. Now... and this is EXTREMELY important... the individual who commits suicide is also not to blame... it is their responsibility, though. This individual is a victim... a victim of bullying, a victim of their perceptions, undoubtedly based on other things. One does not blame the victim in these cases, but place responsibility on the one who acts.
2) What are the characteristics of a suicidal person?
This is where #1 starts to get a bit murky. One who attempts suicide has some significant mental health issues. Regardless of whether or not the act seemed to be a singular event, or something random, it's not. No one attempts suicide on a whim without some mental health issues being present. We have to remember that one of the basic instincts of life is survival. All animals have this, and for someone to behave in a way that contradicts this basic instinct, indicates that something more powerful than that is happening. The suicidal person cannot see a way out of their situation and has decided that ending their life is preferable to living in their situation. Now, this though, in and of itself, may be a sign of that mental illness, since the individual may be completely closed off to other possibilities.
There is no suicide without mental illness. Therefore, this mitigates the complete responsibility of the individual. They are unable to make a rational decision because of their state of mind. This is one reason why I usually suggest to clients to NOT make any big, all encompassing decisions when being completely ruled by their unstable emotional state.
Most suicidal people cannot see past their perceived hopelessness of their situation.
3) How does that suicidal person feel?
Hopeless. Depressed. Overwhelmed. But the overriding feeling is usually intense emotional pain. Consider this. You have a toothache... a bad one. All you want is for that pain to end. This is how a suicidal person feels... even more so. They will do ANYTHING for the pain that they are in, to end. Even kill themselves. For them, death is preferable to feeling in pain.
They are also angry. I have theorized that suicide is often a desire to commit a homicide turned inwards. In many cases, the individual turns that anger towards someone else, on themselves. This is due to self-esteem, depression, and often a long period of feeling emotionally abused or beaten down.
4) For one who completes a suicide, why would that person have not asked for help?
Usually they do, sometimes directly, usually not. Suicidal feelings are very strange and if you haven't experienced them in some direct sort of way, it's hard to imagine them. They conflict with the basic instinct of survival, yet the individual can make themselves believe that they are completely logical. Sometimes it doesn't even occur to them to ask for help: suicide seems like the logical response to their situation.
Sometimes they have asked for help, but do not receive the help they need. Lots of times people believe that these teens are just being dramatic. Rule #1 when dealing with suicidal teens: ALWAYS take their suicidal comments/gestured seriously. ALWAYS. Should I say it again? It is irrelevant as to whether they are being dramatic or not. They are communicating that they are NOT OK. So, it is certainly possible that they did seek help but were not heard.
It is certainly possible that they are in such a hopeless state that they do not believe anyone can help them... so why bother saying anything. Again... their mental health issues overrule instincts... and what they've probably heard over and over: talk to someone.
So, who's fault is it that the girl in the OP committed suicide? No one's. Who's responsibility? Hers. Who contributed to what happened to her? EVERYONE. Personally, I don't care about the blame and responsibility in this situation. It's pretty irrelevant. I'm more about how to prevent things like this from happening, and what to do about them after they happen. Assigning blame accomplishes ZERO. This is about mental illness, isolation, being aware of bullying, and taking our teens seriously. The blame and responsibility is pretty meaningless.
Oh, and for anyone who made any comments about her behaviors. Irrelevant. Nothing to do with the issue at all. I could care less whether she had sex with no one, or 1000 guys. Does not mean that anyone had the right to harass her because of those behaviors... not did it mean that her response to that harassment was OK. This is what I mean. Blame is irrelevant.
I hope this post provided you all with some information on this topic.