in the epilogue how does that narrator indicate that his mother has indeed accepted her past?

Ruth has accepted her past by what she has done through her kids. The list of the accomplishments of each of Ruth's twelve children has an almost biblical resonance. Ruth's children prove to be a testament to Ruth's own qualities of perseverance and goodness, and to the spirituality of her first husband. The book closes on the note of James's close friendship with a Jewish reporter because the friendship is based on a mutual understanding between overtly dissimilar individuals: David Lee Preston understands the meaning of Ruth's actions, and James understands the meaning of David's mother's survival. When Ruth attends David's traditional Jewish wedding, she is no longer a "Jew", but has come full-circle to observe the world she left behind, inspiring her to muse about the other life she could have lived. By taking the road that was less traveled, Ruth became an American and achieved an identity that she defined on her own terms.