So that explains the eBay seller name I noticed, "TheCovidCloset" .  Upon further reflection, my guess was what she does is buy $500 outfits at consignment stores or high-end thrift shops for $50, wears them a few times and then sells them online for $100.  Don't be afraid to ask her for details of what she's doing.  The more reluctant she is to give up information, the more suspicious you should become. 

And the stuff she has owned for years and no longer wants -- wouldn't those go on Schedule D, like selling a used car?  (And people have been doing that for a profit lately.)  There's a box to check somewhere to show if a loss is personal and not deductible.  And the 1099-K will match the Schedule C and Schedule D proceeds.