"She always wondered if she was throwing off their inventory, by buying huge amounts (so that it triggered a "buy more of this!" in the inventory management program) and then not buying any for a few weeks."
She was triggering an inventory control program, but that's not a bad thing given how she shopped, and unless it was an item that spoiled quickly on the shelf having them buy a bunch to offset the demand she created is not a problem. To tie it back to the thread, I don't think she was doing anything SSish to buy like this, and she shouldn't change her shopping habits just because of inventory software. The software will adapt to her habits quite nicely, as it's designed to recognize stuff like this. In fact, she'd be doing them a favor to pick a behavior and stick to it so the software can lock down the pattern.