Oh, Mum.
I went through the exact thing but it was 2nd grade (age 6-7) through 9th grade (age 13-14). By 9th grade I was so depressed from the year upon year of playground bullying, harrassment, tormenting and ostracization that I completely gave up. I was too naive to understand the concept of suicide but if I had, it would have occured to me. Smuggled novels into all my classes, made straight As in English because I loved it, flunked every other course and had to repeat the year. It was a nightmare, and I know schools are no better, perhaps even worse, today.
I send much compassion to you and your daughter.
Like you, my own very painful childhood was retriggered by my daughter going through the EXACT same thing. At around the same age I had been at its worst, she said to me, "I don't even feel like living." And she too was quite young (around 9)--and didn't yet know the concept of suicide.
I have two thoughts, don't know if they would help a little. My daughter developed friendships earlier than I did, and developed compassion. By high school she did have a close best friend, and she also deliberately sought out the most picked-on, reviled girl at the school and embraced her seriously as her friend. Other kids began to notice her kindness and she found a small circle of good people. Most nonconformist, but all essentially kind and sensitive. She also bonded in those adolsecent years with our Unitarian Universalist youth group, and I have never seen her happier. That curriculum is completely about love and tolerance, and after her years of pain, it was amazing to see her happiness with them. She belonged. So what she didn't get widely in school, she got there.
The other memory is that once in elementary school, a girl was picking on my D mercilessly. I called the teacher and explained what was happening and they said oh thank you, we will deal with this. A week later, no letup. I called the teachers again and mentioned that I would like to speak to the other girl's parents and the teachers said oh NO, must not do that...WE have to be in charge of that. No change. A few days later I happened to be at the school when my D's class was coming out of the auditorium. I spotted the little tormentor, who knew me (small school, same birthday parties) and saw my chance. I said Hi, "Susie" can I speak to you a minute? Sure, she said, and I ushered her around the corner. With no threat of harm but with my FIRMEST SuperNanny voice, I bent near her, looked her right in the eye and said, "I don't care if you don't like my D, you do not need to like her, but I do not want ever again to find out that you have pinched her, tripped her, pulled her hair or done ANYTHING to hurt her again. If you do, I am going to call your parents immediately. Do you understand me?" She nodded like mad and that was that. The next week I went to pick up my D and she and "Susie" had their arms draped around each other and Susie even started inviting her over to play. (I almost felt that Susie was grateful that somebody stopped her...)
Long story shorter: if the insitution will not step in, I advise dealing directly with the harrassing child/children. With complete control of yourself, but without begging anyone's permission. Fer Godssake, where are the grownups when this is going on? Wringing their hands and worrying about diplomacy, while some child is having their heart broken over and over. Grrrrrr.....
Sorry to rant on and on, Mum, but I do so understand what you and your D are going through. It will pass...but lord, I know how it hurts. (The euphemism of "harassment" often is a cover word for straight-up bullying, abuse, and sometimes even violent behavior.)
Hopalong