The veteran star, famed for her role as Princess Leia, died unexpectedly in December, 2016, but director J.J. Abrams was able to cut together unused footage of Fisher from 2015's "Star Wars: The Force Awakens" to resurrect her character for key scenes in the recent "The Rise of Skywalker".
Lourd, who portrays Resistance member Lieutenant Connix in the sci-fi blockbusters, helped Abrams and his team complete the sequences by taking part in the Leia shoots, and she admits it was truly bittersweet to fill in for her mum.
"It's literally like a gift from her, or her forcing us to make her the star of the movie - probably both!" she laughed in new behind-the-scenes documentary, "The Skywalker Legacy".
Lourd added, "Being back has been incredible, painful, surreal - all of the adjectives that you can come up with, probably, I felt."
Abrams later used Fisher's earlier film clips to digitally replace the 27 year old's face with that of her mother.
Production on "The Rise of Skywalker"'s Princess Leia scenes was also an emotional experience for leading lady Daisy Ridley, who needed to collect herself after filming.
"The reality of having to do a scene with someone who isn't actually there was very difficult," the Brit shared. "I sort of had to walk off and have a moment."
And Abrams insists he will forever be grateful to Lourd for giving him her blessing to bring Fisher back from the dead onscreen.
"To know that we were doing this with her at our side, that's something that I will always be grateful to her for," the director said.
"The Skywalker Legacy", which details how filmmakers incorporated unused Fisher footage into the latest movie, will be released to coincide with the digital launch of "The Rise of Skywalker" on March 17.