Sorry, thunder. The dcs here have certainly kicked out occasionally whilst wriggling away from a nappy change, or in a tantrum, or very occasionally whilst swinging their legs in the pushchair and caught someone accidentally, but by three, I wouldn't expect any child to kick an adult stranger in a queue. The child in question wasn't in a pushchair (I'm a bit confused - I thought she was originally, so had thought it might have been an accident, but later the op said that plus chairs weren't allowed in the queues, (in amongst the laborious 'we use the pushchair as a punishment' routine) so I'm guessing she was just kicking.
Bitten? One of them did once. He didn't ever do it again. (He bit his sister). The other two, nah. Some kids are biters, but again, it isn't all kids.
Hit, kick or bite a stranger in a queue? Um, no. And I have two with sn. To say you can't keep an eye on a kid in a queue is nonsense. Parents of kids with sn are hyper-vigilant, have to be. Because you know that something unexpected can happen. Eyes in the back of your head, and all that.
We are all human though, and we do get distracted occasionally - but if a child lashes out, kicks, prods, (bites?!) or is otherwise doing antisocial stuff that is affecting other people, I fully expect them to be told off for it. Loudly. By other people. And then I assume the mortified role and apologise profusely, and remove my child from the scene.
Why are adults not allowed to tell children off for hurting them? I'm completely baffled. I quite like it when other people make my job as a parent easier, by disciplining my kids for me.
it makes my job much easier. It IS embarrassing... As it reminds me that I'm not managing to fulfil my parental responsibilities and my kids have upset someone, and I should have been able to prevent it, but I blame myself for that, not the poor passer by who was offended by my unruly mob. I self-flagellate for days, but I get over it. And it makes me more attentive in the future 
I'm betting the op will keep a closer eye on the dd from now on, however much bluster she can muster and try to make light of the fact she wasn't paying attention...