Actually, it used to be standard that when you presented to an ED with significantly elevated blood pressure you would automatically have your optic discs evaluated. In most EDs this rarely happens anymore, so I can't imaging an optometrist in a drug store is going to routinely be looking for this - particularly in an 8 year old. If this poor child had presented to an experienced pediatrician's office, and had complaints that suggested the diagnosis, it might have been made earlier.
I believe they determined that she could see the problem but neglected to diagnosis it.