The phrase is clearly a metaphor for the original unpolished state of diamond gemstones, especially those that have the potential to become high quality jewels.
PDCR has taken Terra from her "unpolished" state and produced a beautiful gem, reinforced by her unique diamond pattern graced so eloquently on the crown of her head.
Terra came into rescue as a scared, shy stray who wouldn't even walk on a shiny surface. With a lot of care, and patience the team at PDCR is seeing the dog Terra was meant to be, the dog she should have been all along, but was forced into hibernation by lack of basic care, food, shelter, love. Emerged now is a happy, silly girl, discovering her inner retriever. Terra loves her people, all sizes, is playing with other dogs and is being respectful in the house.
As with most diamonds in the rough, Terra is passed over, and dismissed. We all know that every dog is worthy of a home, and Terra is certainly no exception she just hasn't found that person who sees her potential. Who wouldn't want this polished gem? - all she needs is a place to be set.