You're creating a huge security problem: First, someone has to engrave it, and see your private key. Then, since it's jewelry, she'll wear it, and more people can see the private key. And jewelry is the first thing thieves take, making it one of the least secure places to store value in.

I like the idea though If you use BIP38 encryption with a strong passphrase, and keep a backup of the private key, it could actually work.