“Priscilla is adamant that she has a valid case and that she will prevail in court. Riley and Priscilla aren’t communicating at this time, but have been in communication through lawyers.
The Daisy Jones & the Six actress - who has a baby daughter with husband Ben Smith-Petersen - is keen to settle the matter privately without a lengthy legal battle.
The insider added: “They are both gearing up for court, [but] Riley would prefer to settle this dispute privately.
“She is heartbroken that this has turned into a public matter and knows her mother would never want this. Riley is very stressed at the moment and has been trying to keep a positive attitude and outlook ahead of her new series coming out.
“Her daughter and husband have been keeping her in good spirits.”
As for Priscilla, the insider said the 77-year-old star is doing what she feels “is right in her heart” and is determined to pursue the matter because she’s still “convinced” the 2016 amendment was faked.
The source said: “She is convinced that old documents had been forged.”
Lisa Marie’s spokesperson previously confirmed Graceland would go to her daughters Riley, 33, and 14-year-old twins Harper and Finley.