The Orange County Sheriff’s Department told PEOPLE that the teen died of an overdose, which is what TMZ first reported.

Patridge, who is 38 years old, posted sad pictures of her niece and herself together over the years on Instagram on February 14 to say that her niece had died.

“My heart hurts to even write this. My beautiful niece is now in heaven,”Partridge wrote in the caption. “I know [it’s] not goodbye forever, but it is the hardest to say goodbye for now.”

At the end, she wrote Sadie a note that said, “We will miss you and cherish every single moment we had with you. Rest in peace Say Say!! We love you forever & ever! ✨🤍🙏”

In the post’s comments, the Hills actress got support from people who used to work with her. Kristin Cavallari wrote, “OMG this kills me.”

“So so sorry for your loss Audrina. This is heartbreaking,” Brody Jenner commented. “Sending love to you and the family.”

This post, which included a picture of her late daughter Sadie, was made by Casey Loza, Patridge’s sister and Sadie’s mother.

“Sadie Raine Loza has left this Earth for the heavens,” she captioned the post. “Writing this was the hardest thing I ever have had to do, not knowing the right words I’ll leave you with this, Sadie liked to remind me that the first law of thermodynamics aka (Law of Conservation of Energy) works in all spheres of life…..’Energy cannot be created or destroyed, it can only be changed from one form to another.’ “

After writing about how her daughter’s life will live on, Casey said, “Transformation is a better word than death. Her story will save countless lives, her memory will never be forgotten. Rest In Peace you brilliant starseed. You’re with your creator. We will miss you dearly. I love you.”

As a way to show his sadness over Sadie’s death, Casey’s husband Kyle Loza posted the same selfie of the girl the next day.