Oh dear, I really feel for you and your DD. Some teacher and especially heads seem to be completely useless.
My girl is in Y5 now and in Y3, a lad started constantly going up to her, leaning forward right into her face and glaring at her. She told me and I said to tell a teacher and to try to ignore it. She told one teacher, who told her not to be a tell tale and another said, "Oh dear, just ignore it."
We were in the park and he came up and did it, she said, "You see? I told you he keeps doing it!" I moved us away from him. He did it again, in front of me and I spoke to his mother, who turned and walked off, with no comment.
This had started in the January, but I hadn't realised just how bad it was, partly because I work away, for long periods. FF to Y4, last October. I got home and she told me that our girl was in the time out book and banned from playtime for two weeks. He'd gone up and done it in the playground and she'd stuck her tongue out, which was seen by the headmaster; he called her a bully.
My wife and her sister (moral support) went in for a meeting, where the head looked at the ceiling, twiddled his thumbs, wouldn't make eye contact and kept asking, "What's she doing here?" He accused our girl of a campaign of bullying. When she stuck her tongue out, he asked the lad if he should put her in the time out book.
Also, my girl and her friend were making a video, in the park, after the tongue incident. The boy ran past them and then ran to his mother and said, "Oh, she said she's going to put it on Youtube with my name and address!" (complete fabrication) The mother snatched the phone away and tried to delete things, so my wife demanded it back. She told the boy's mother that she was sick to death of his behaviour, the mother said that she was going to tell the school that our girl had been continuing to "bully" him.
My wife said fine, I'll tell them what really happened. The other mother said, "Don't worry, son, Miss S. is a good friend of mine, you won't be in trouble."
I spoke to my sister, a high school nurse and she asked one of her year heads. She said that the HM was grossly unprofessional and wondered if he'd had any lived experience as a human being!
I went to see her class teacher, who told me that the HM had said that the boy was "only looking." I explained what I'd seen, asked if she'd seen the glaring and named the two teachers who'd ignored her. She admitted that she hadn't. I told he what my sister's colleague had said and that the other mother had said she'd use her influence.
That sat her up. I said that I was sure it wasn't true that she would do anything like that, but that it could make her look bad, if people believed it. The next day, she phoned to say that the teachers were primed to look out for him hassling her and that they'd been put on opposite sides of the class. Also that the head had taken them aside and given them a homily about being kind.
Why should she have to be kind to a nasty little shit like that?
Anyway, she asked me if I thought the HM was wrong and I said yes, but I think it's sorted. I told her not to say anything, so of course, she went up to the HM the next day and said that; he said, no, you're both wrong and you're a bully. She was distraught.
I spent a week composing a letter to the school governors. I had to keep toning it down, as it was clear I was blazing.
I eventually got a bland reply, to the effect that the head had dealt with it, be kind, blah blah, that's not his reading of it, he's very experienced etc etc.
I told her that it was her last year there and to just try and get through It's spoiled her experience of school. She's at middle school now and got into a bit of trouble in the first few weeks, as she was resentful and under the impression that all the adults are against her. They've been much better in trying to work with her and she only tends to have one tantrum a week, when it's time to go to school!