Hi, firstly sorry for your stress, as if there aren't enough difficult situations to be dealing with just now.
I'm not a doctor, but I imagine if you went home quickly and washed etc. then your toddler will be ok, that is even she touched his face at all?!
With regards to the woman trying to touch your child's face, I am sure that she meant no harm, just probably wanted to be kind and reassuring. Admittedly not in keeping with the current 2 metre sentiment but I think that she may well have acted instictively.