I would actually love to see her sue.
She pays $75 or so to file a small claims lawsuit. It piddles around, eventually makes it to court. You walk into court with the UPS image of the package on her front doorstep. The judge asks her if that is her house. Under oath, she says yes. Case is dismissed with prejudice. She’s out $75.
If the only accept cash but never have any cash on hand, then where is all the cash they’re collecting multiple times per day going?
Also, why not agree at $80? Why agree to $79 in explicitly cash? That’s always going to be a pain to scrounge around. It requires 4 ones and either 3 fives or a ten and a five. No matter what, it’s a painful wad.