49, I usually don't go right to ditch the bitch, but in this case, exceptions can be made. You made it, "link by link", and she says it isn't unique enough, take it back, and hold onto it for the next woman who would actually appreciate it.
Maybe the necklace wasn't particularly unique looking, and she assumed it was bought? Make sure your girlfriend knows how hard you worked on it, and hopefully she will be grateful. I'm not excusing her rudeness, just trying to explain it.
It might be unique in the hand-made original sense but necklaces in general are common gifts, and therefore, not unique. This lady seems high maintenance.
Or take a class with him. Or go to an open studio. Couples who do fun things together and share each other's interests are strong and healthy couples. Generally.