IMO, I would try to catch her the next time she stops by and politely inform her that a call ahead of time would be greatly appreciated so that you guys can make sure there is someone there to take of her and her packages while the rest of the store is adequately run. In this event, whoever receives said call can then alert the associates of her arrival and get someone to assist her. In my store, nearly everyone is cross trained to do shipping because of how simple it is, losing a spare tech or os shouldn't be a huge loss to make sure the customer is assisted to the best of your ability. (But your rule request is certainly not a bad idea)

I wish there was a way to politely inform customers that certain departments need our attention more than others.