Her reciprocal accusation is probably just a knee jerk reaction at being caught and shown up - cornered animal-style.

If you've got to back tomorrow, do you have an old invoice for one of the pieces in question going back a while that you could take with you?

With all of my orders, I print the invoice alongside photos of the item and any notes about sizes, mods etc. written on it (I take a screen grab and the photos and print them on one sheet) and staple that to the postal receipt, copy of the customs forms etc. That way I could show, with photos, anything I've sold with postal proof of when it went etc. If you had such a thing from 4 years ago it would show how long you'd been making the piece.