Maybe I'm in the minority but I'm not seeing a business here.  Cleaning out the attic/garage is not a trade or business.  If she were buying stuff in thrift stores and then selling them online then yes, that's inventory and presumably there's a profit motive.  But selling your own (kids) clothing sure sounds to me like a non-deductible personal loss.

I reported one last year in other income (Sch 1 somewhere now?)

1099-K from Paypal $xxx
Personal items sold on ebay at a loss -$xxx

Schedule 1 Line 8 $0

Won't know how it went until 4/16/24. 🙂

Rick