That question on the ERIC website refers to a child having an individual health care plan, a child who has just randomly had an accident is unlikely to have one of those.
There may not be a legal requirement for two staff members to be present when changing, but many schools have it as their policy for good reason, and staff are required to follow policy.
Maybe if there are staff shortages the policy should be changed, but at the same time there's a fair argument against expecting teachers to change soiled children alone. If there were no baby wipes available, then staff wouldn't have been able to get her properly clean in school anyway, so it would still be wise to ask a parent to come and ensure she was clean.
I'm not saying it's ok for a child to be left so long in that situation, it's not, but I think it's highly unlikely to be the teachers fault that this happened. I think you need to ask why your child was unable to be helped. Is it normal procedure or was it because of bad timing and there was simply no one available to do it? Ask the headteacher what the school policy is, and why the teacher made the decision to call you instead of changing her, or instructing her how to clean herself. Does the school have equipment available like gloves, spare bags, spare underwear and baby wipes? (I know you sent in spare clothes, but the policy should be the same for all children, even if it means children going commando with PE kit). Why weren't you allowed to change her at school so that she could go back to learning asap? As a PP said, your being at work is irrelevant as there could be any number of reasons why a parent can't be at school within 15 mins, that shouldn't affect them making decisions that are in the best interests of the child.
I hope your dd is ok and you can get it sorted so you both feel better.