"It's completely surreal. There's no way to really explain it," Lourd told host Ellen DeGeneres. "It's so hard to talk about."
"I don't know, if I say that I'm doing good, I'm too happy. And if I say that I'm not doing good, then I'm a mess," she explained. "So it's really hard to know what to say about it because it is just so surreal and impossible to deal with."
Fisher died Dec. 27 at age 60 following a heart attack and Reynolds died of a stroke at age 84 the next day. Lourd said she was grateful to co-star with Fisher in Star Wars: The Force Awakens prior to her mom's death.
"It was incredible," the actress said. "I'm a big believer in things happening for a reason, and I think I ended up in that movie for a reason. It was really incredible for us to get to have that experience together."
Lourd previously said in the September issue of Town & Country that it's a challenge to honor Fisher, who played Princess Leia in the Star Wars films, and Reynolds, who starred in Singin' in the Rain, while forging her own path.
"I love being my mother's daughter, and it's something I always will be, but now I get to be just Billie," she said. "It's a lot of pressure, because she had such an incredible legacy, and now I have to uphold that and make it evolve in my own way."