Little Bo Peep wears a necklace with a small stone heart.
"A chain so thin it was almost invisible rested around her neck and was tucked neatly away into the top of her dress. She pulled the necklace out and showed him the small heart-shaped rock hanging from it."
This is the part of her heart that holds the pain of missing her lover and child. Hagetta cut it from Little Bo's heart to spare her the pain, using the same spell that her sister Hagatha used on Evly and her Heart of Stone.
When she dies, the little stone heart cracks, a symbol of her heartbreak.