Upon a closer reading, you may find that she is in the business of selling consignment items from her friends (Schedule C) as well as her own personal items for FMV that is less than original cost.  One can either panic in these circumstances, running around like Chicken Little and screaming "the cloud is falling," or instead realize that IRS doesn't have the staff to open last month's mail, much less pester small-time online yard sales.  

The 1099-K is one big bluff to make people think IRS cares enough to deal with the nuisance.  But let's say she made $3,000 selling $30,000 for others, and the rest is just static.  Those who play "Trick the Computer" will probably report all sales as gross receipts, for the sake of matching the 1099-K, and then subtract out the personal stuff as inventory valued at date of conversion from personal use.  This is neither truthful nor accurate, but these days who cares?