In the "Scream Queens" star's post, which featured a throwback with Fisher, she opened up about how the day can be complex.
"Even though I’ve been a mom for almost 3 years and now have 2 kids of my own the first thing I think of when I hear happy Mother’s Day is her," Lourd captioned her post. "Even though it’s been over 6 years since she died, when I first wake up, this still feels like her day - not mine."
She continued, "But as the day goes on I remember it is my day too now."
Lourd went on to describe her mindset in sharing the day with her late mother.
"I am a mother to two magical little creatures that I adore to my core and there is nothing that brings me more joy than being their mother," she wrote. "And even though she’s not here, it’s still her day. It’s our day now."
Lourd said that was "both sad and weirdly beautiful at the same time" and went on to say that the holiday "can be many things."
"With the magic of life comes the reality of grief," she wrote. "It is all intertwined ... So like I say every year. Happy Mother’s Day but also griefy / sad / lonely / estranged / frustrated / etc Mother’s Day! Mixed Emotions Mother’s Day!!!"
She shared her thoughts for anyone in need of support on the day: "You are not alone."
Fisher, who died at the age of 60 on Dec. 27, 2016, was posthumously honored with a star on the Hollywood Walk of Fame earlier this month.
Lourd accepted the honor on behalf of her late mother and delivered a sweet speech on her mother's impact at the ceremony.