Custom offer to buyer?

I’m a FBM seller, I sold a Waterford champagne flute but accidentally shipped out a Waterford ornament. My buyer contacted me asking to swap but expressed an interest in the ornament as well (prices similar, flute just under 100 ornament just over). They are both rare items and are sold out currently on Amazon. I am happy to sell her both and at a discount to make up for the inconvenience but I’m looking for a way to sell her the ornament/flute again without making the listing public and risking someone else purchasing the discounted priced rare collectible. Any suggestions? At this point no return request has been opened and buyer has been communicative/friendly.