Probably part of a bone. Considering the size of bones it might be part of her hip or thigh bone. They tend to have the most protection from the body. But, I really don't know.
I never was big on these relics.
There is a small metal box in St. Peter's in Rome. It's one floor down below the street level. It is supposed to be the remains of St. Peter. It say simply: Here lies Peter.