You are overthinking this and being just a little PFB. Her rubbed "little feet" can't have hurt that much or surely she would have told someone, or told you the minute you arrived rather than not giving them any thought until you noticed?
I don't get why you got "really cross" - this happens with children all the time, your DD is one amongst hordes, she was dressed, the shoes were an oversight, get over it. Maybe when they agreed to get them changed they meant costumes, meaning clothes, and didn't even consider shoes? I wouldn't have as long as they were dressed.
Or and here's a thought you could avoid such awful situations by teaching her which feet her shoes go on. She's in reception, maybe the teachers thought she would know this and changed her clothes but didn't check her shoes.
I tend to like the "There is a 'L' on your left hand and a 'L' in your left shoe" (drawn in with pen) "Put your 'L' shoe on the foot below your 'L' hand". Works well with Reception age kids.
In case anyone is wondering if you hold your left hand upright in front of you and look at the side, then drop your thumb - ta daaaaa! There is an 'L'. There isn't one on the right so no confusion. I also find this works well for adults who still haven't learnt their left from their right.