"I do like to think I live a very private life but I kinda felt like I wanted to share with you where I’m at,” she wrote to her 237,000 followers.
"On the 11/8 I had just received news that my sister passed away. I've been trying to process that on my own being stuck in a Sydney lockdown without my family, off-country and by myself.
"I’ve thankfully had huge support from production and friends working tirelessly to get me back into WA."
On Friday, two days after her sister passed away, Brooke was granted a G2G pass to travel to her native Western Australia so she could mourn with her family.
"I truly believe in life that when there comes good, comes bad. This felt like one of those moments, but I can’t believe the huge support I’ve had," she said.
"I feel, honestly, so grateful. I wouldn’t be coping if it wasn’t for production, my friends, my loved ones and (my dog) Cobar."
The youth worker said she didn't feel the need to share the tragic news with her fans, rather that she "wanted to".
"Just to say… I know we’re all doing it pretty friggen rough with the current world climate," she wrote.
"Though look to the sky and lift your head up. We will get through this."
Brooke has made history as the first Indigenous and openly bisexual woman to star as The Bachelorette.
It's understood that filming on the upcoming season wrapped last week.
The proud Noongar-Yamatji became a fan favourite during her stint on Nick 'Honey Badger' Cummins' season of The Bachelor in 2018, where she quit in the final week.
Brooke has been candid about losing members of her family at a very young age, and how it inspired her to do more work within the Aboriginal community.
"My biggest passion in life is mental health, from working and growing up with a lot of drug and alcohol violence in my childhood really," she told SBS' Noongar Dandjoo.
"I grew up in a country town in Carnarvon. I spent my childhood there up until I was about 11, when my mum, unfortunately, passed away—she committed suicide."
She revealed that her grandmother died only a month later, which saw her and her sibling placed into foster care.
"All my brothers and [me], we didn't really have a lot of strong role models so creating that myself was my inspiration," she said.
Brooke also revealed that she felt she didn’t have ”stability that was normal”, and she was surrounded by things that kids “shouldn't be exposed to" at such a young age.