YABU.
She's probably encountered lots of parents who let their children pull things about, run around, drop things etc. I know I did in a supermarket. Parents letting their kids eat the (to be weighed) pick n mix, or worse, put their hands in the stands and eat them. Pull things about, drop jars, run about, leave then alone while they try on clothes etc.
It's a common thing in retail for some parents to behave like this and leave their children to roam. While by no means the majority, its common enough to cloud people's views. Letting your child pull things about and leave them in the floor, isn't ok. It might be what kids do, and it might be ok in a nursery, crèche, home, child's section of a library. A shop is none of those things. It doesn't matter that she's a young child, or it's what children do. It's not a nursery where children are allowed to do those things.
From her perspective, your child was pulling out toys while you were looking at books and not intervening. Most parents I've encountered would have walked off without tidying. As you weren't stopping your child, presumably and understandably, she thought you the same.
No one expects children to behave perfectly. They tantrum, cry, shout, it's normal and expected. What's also expected Is that parents control their children