Sparkly I don't think you sound like a helicopter parent. Those are all very valid reasons. I have a lot of respect for HEs as I too have felt extremely disaffected by school life - both as a pupil and witnessing how school has dealt with my own children and their peers.
But, as you say, there are unpleasant judgemental people everywhere and the best thing you can do for your daughter is to teach her how to spot them, handle them and not let them diminish her. To do this, she needs practise with them.
Whilst we don't HE, I do an awful lot of things with DC that HE families do - lots of museum and gallery trips, workshops on fun things, craft and science activities at home, reading aloud together.
Something interesting happened with DS2. He had a teacher who hated him. She was pretty open about it, even to me. I left parents' evening in tears. She was and is a cruel, unpleasant woman. She targeted one or two boys a year and DS2 was her chosen child that year. He has now forgotten how miserable she made him. How long faced and frightened of school he was that year. How he had physical symptoms of stress (as did I). What he got from her was that in his desire to please the old witch he moved from bottom of the class to near the top and has stayed there ever since. She never rated him, always scorned him and dismissed his efforts. But the following year, a fresh teacher saw what he had done in order to try and win her approval and was so complimentary about his ability.
So... I've felt over-protective in the past but with long sight, can admit that even the nasty teachers have helped my DC along the way to stand up for themselves.
(Incidentally DS1 also had this teacher and was severely bullied in her class by her favourite child.) As the bullying escalated, he ended up doing martial arts to protect himself. He once, just once in all those years, hit the bully back, with his martial art prowess and has never been touched by him again. DS1 ended up getting into the secondary school the bully had set his heart on but didn't make the grade, and DS 1 is also now a brown belt.
Long winded way of saying - we don't have to be there 24/7, or to be the sole influence in our DCs lives to help them cope. Protecting them in the short term may not help them in the long term. One day they'll be out there in the world rubbing up alongside with people who are physically, mentally and emotionally damaging as well as kindhearted, strong minded lovely people.