A mother brings her four-year old son to the pediatrician. She tells the doctor that her son has been vomiting

A mother brings her four-year old son to the pediatrician. She tells the doctor that her son has been vomiting ever since he ate a hamburger from a local restaurant at lunch. The son eventually dies. The parents later sue the restaurant for serving their son contaminated meat. The mother is too grief stricken at trial to testify. May the doctor testify about the mother’s statement? Is there anything in Rule 803(4) that requires a statement made for medical diagnosis or treatment come from the person diagnosed or treated? Does the mother’s incentive not to lie to the doctor who is treating her son, make her statements reliable?