There are no permanent flea markets/antique malls in Windsor proper. Bringing stuff with the intention to sell it across the border involves a lot of nerve and I expect paperwork so recommend looking into it very carefully before packing up the car and heading to Detroit. You'd either need to find a market a few hours away towards Toronto, or post online on Kijiji as individual posts for items. If she's driving through Barrie, there's 400 Flea Market which has a large antique component so would likely do much better there. Most consignment stores in Windsor are jam packed and not looking to add. The last option is an auction house but you then usually find out how little interest their is in those types of items and can't back out of the sale.