Except, for those who were bullied, it's still something that impacts their lives. I could give you names, places and often rough dates of times I was bullied throughout my secondary school life. I left 20 years ago. I have not forgotten, as much as I would like to. Why should the bullies be able to forget if their victims cannot?
Spot on.
I think even the word 'bullying' can be open to interpretation, but we're not talking about 6-year-olds shouting and calling you a smelly poo-head in the playground, this was a 15yo - not that far off an adult - and a protracted, calculated campaign. If the word 'tormenting' or 'abuse' were used, people might understand somewhat better.
Yes, people can change, but their past actions and the scars that they leave on their victims can't be deleted. You can start to build good relations with new acquaintances, but you have to accept that you deliberately almost certainly destroyed any hope of good future relations with your past victims.
If you are truly repentant, you can always try and find a way of getting in touch to say that you understand they will probably not want to have anything to do with you and you don't expect a reply, but you want to say just how very sorry you are and how much you deeply regret what you did to them - as the PP's DP's erstwhile bully did.
She may be a completely reformed character, but she might be the same (as the OP suggested appeared to be the case) or she might even have got worse over time.
Something quick and relatively impersonal like being served in the corner shop might be more tolerable, but something as intimate and long as a session at a salon, with somebody who has the ability to hurt you with scissors and/or deliberately make a complete mess of your hair, is often something you might be reluctant to trust a neutral stranger with at first, let alone somebody you know HAS wilfully hurt you in the past.
If she's renting a chair in the salon, she's likely self-employed. Of all workers, those who are SE have to understand that their very livelihood depends on their reputation - current and past - whether it relates to the quality of their work, their reliability, honesty, personal integrity or behaviour.
You wouldn't employ a builder with a reputation (or whom you have previous experience of) for building walls that crumble and fall over within the month or a plumber whose work has directly led to several home insurance claims for flooding - however charming or lovely they were as a person. It works the other way around too.