The designer Emily P. Wheeler, who runs her own jewelry company in Los Angeles, found Ms. Miller on Instagram and began consulting with her a few months ago. “There is an overwhelming amount to learn around ethics and sustainability in the fine jewelry industry,” the designer wrote in an email. “I wanted help defining our goals and standards, so that we could implement better practices moving forward.”

Through Ms. Miller, Ms. Wheeler found out about Moyo Gems, a project that works with women miners in Tanzania and Kenya — where much of the mining is predominantly done manually, with limited equipment — tracking gemstones from miner to market.

“I created a version of our signature Chubby Rings with one of their garnets,” Ms. Wheeler wrote, adding that, “At the moment, Christina is more focused on helping us source responsibly ourselves, rather than sourcing stones on our behalf.”