Credit: Michael Kovac/FilmMagic; Amy Graves/

Casey Johnson's purported fiance Tila Tequila says she plans to seek custody of the late heiress' adopted daughter Ava, 3.

Johnson's mother, Sale, currently has custody of the girl (whose godmother is Tila's enemy, Nicky Hilton), but Tila (real name: Tila Nguyen), 28, says that's not what Johnson wanted.

"Her last wish was to have me have Ava," she tells Extra in an interview airing Wednesday.

Tila -- who was not invited to Johnson's funeral Tuesday -- says she wanted nothing more than to see the heiress before she was buried. (A source previously told "She wants so badly to go to the funeral.")

"She's not resting in peace right now," Tila tells Extra. "She has come to me in my dreams."

Johnson, who suffered from diabetes, was found dead Jan. 4. at the age of 30.

Though a cause of death has yet to be determined, Tila says Johnson "had a sleeping problem" and is convinced Johnson's death was accidental.

"I know for a fact; Casey was so excited for our life together," she says. "I know for a fact it was not suicide."