As a qualified professional counsellor myself, I had a client in her twenties who absolutely despised herself for things she had done to others when she was young. Without going into too many details, one of her victims had been hospitalized. She genuinely wanted to track down and make a heartfelt apology to this person. Having been bullied myself, I was well aware of the potential to re-traumatise and we looked at who would gain what from her doing this. She was already working in a care environment, and wanted to become a counsellor. All I can say is that by the end of our time together, I truly believed that she could do so, and indeed be very good at it.
Counsellors are often referred to as "wounded healers" and while she was not bullied by her peers, she had become a self-loathing bully in response to her upbringing. Not to excuse what she did, or what was done to you, but you almost certainly do not have the full picture.
I was reading the stuff about Chrissy Teigen and things she had said on social media, and been reminded of my own bullies - there were several different groups. One girl has since apologised to me, and I'd go so far as to say we are loose 'friends', but I could not bring myself to attend her wedding when invited, knowing that some of the rest of her group, and one girl who had physically attacked me, would be there. I just felt that it was a step too close to making it all okay for them, when in truth it never was and never will be okay by me. 40 years later, I recently had a nightmare about one incident.
I totally understand why someone's victim and anyone who knew the 'old' version would be sceptical, but truly believe that sometimes having been to "the dark side" and seen what you are capable of in those moments, enables you to better manage your responses later in life. That fear of yourself somehow keeps you in check. If she can help someone else manage their baggage/emotions better than she did at that time, then she earns the right to forgive herself, even if others find it hard.
I'm sorry for what she put you through, but if she is a BACP accredited counsellor, then she will have had a lot of therapy of her own, and had regular feedback throughout her training to help her identify any residual potential for manipulative/bullying behaviour. It's not 100% failsafe, but she will have spent a great deal of money to achieve the position, and had to face up to her past behaviour. It doesn't help you, but she may be able to help others, and as a changed person, I know for a fact that she also lives with what she did every single day.