"She is going to consignments and reselling, but also reselling personal things."

Then your client is doing partly what that reference's client is doing, and partly not. Your client seems to have three activities:

Selling personal goods, so FMV is whatever it sold for, or use the web-based Used Goods references. That determines COGS. The activity would show net $0.

Selling friends' goods on their behalf = intent to make a profit (commission) on it = consignment business.

Buying on the open, used goods, market = now you have an actual COGS to the timely sale, unless there is personal use in between. As long as this is "bought to sell it," this would be a business operation.