Do not be nice and 'oh so lovely, reasonable and understanding' about this toward school. Do not seek validation from school and do try not to be that mum. You have to tackle this with utmost calm and determination, no-one else will advocate for your lovely dd.
Below is a link to the DfE school safeguarding guidelines, read it thoroughly, print it out and go in with your husband or another family member so that you have a witness to your conversation and someone who has your back and can reinforce if needed. I speak from experience by the way.
After each meeting or phone call with school, write down the minutes e.g, what has been discussed and next steps that have been agreed. Ask for a follow up appointment 2 weeks or later and do not ever be fobbed off. Schools are notoriously crap at dealing with bullying, especially bullying from girls.
The school have a duty of care to both girls and are currently failing both. They need to put an action plan into place that prevent anything like this from happening again. Maybe the other girls needs 1-2-1 supervision to keep her away but most certainly she needs an intervention to teach her social skills. Rubbing nettles on another child's skin is peer on peer abuse (point 29 in the linked PDF).
The fact that your dd is disabled adds an extra layer of worry and the school could, if they don't tackle this effectively and immediately, be breaching equality legislation.
Do not, under any circumstances, approach the other parents. Communicate with the school and push as hard as possible. Be careful about gossiping about this to other parents while all this is going on.
Unfortunately even nice schools often just seek to keep the bullied child's parents at arms length. If you are calm but persistent it's harder for them to ignore you.
I wouldn't be surprised if the girls who is causing your dd such grief is being bullied at home, because that is not 'normal' behaviour, very wilful and huge lack of empathy.
assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/912593/Keeping_children_safe_in_education_part_1_Sep_2020.pdf