Calls from the AP to people representing Mary and Robert Kennedy were not immediately returned on Saturday.
The 52-year-old mother of four hanged herself on May 16 in a barn by the couple's home in New York's Westchester County amid bitter divorce proceedings, after he won temporary custody of their four children, ages 11 to 18.
Since he filed for divorce two years ago, her battle against drug and alcohol addiction included an arrest for driving while intoxicated. An autopsy report showed she had antidepressants in her system when she died.
In a court affidavit linked to their divorce, Robert claimed his wife beat him, threatened suicide in front of her children, ran over the family dog and drank until she passed out.
The Richardson family said his account was filled with lies.
They lost a court fight to bury her at a location of their choosing.
The Cape Cod cemetery is in Centerville, near the Kennedy compound in Hyannisport.
Mary Kennedy's relatives did not attend the funeral Robert Kennedy organized in Bedford, N.Y., the Westchester County town where they lived. After her burial, the Richardsons organized a private tribute to her in Manhattan.
Photos show her new grave near the cemetery entrance is marked by small religious statues and two American flags.