Influencer and Model Niece Waidhofer Dead by Suicide at 31

Model and influencer Niece Waidhofer -- who often worked to help her followers through their mental health struggles -- has died by suicide ... TMZ has learned.

Niece's family tells us, "Sadly, Niece took her own life after a long battle with mental health issues." The 31-year-old died in Houston, TX.

Her family says, "She was very open with her followers about her struggles, even wanting to help followers who also suffered." We're told a non-profit called "Peace from Niece" will be established in her honor, and the org will benefit mental health awareness and provide grants for mental illness research.

Niece's family says she took pride in the fact she wrote all of her Instagram posts herself, and shot the majority of her photos without a professional photog.

As for the circumstances surrounding her death, law enforcement sources tell us they got a call from a concerned family member last month to check on Niece at her Houston-area residence ... and that's when she was discovered.

Fans of Waidhofer -- who had amassed 4.2 million followers on Instagram -- became concerned when she wiped her account of almost all of her photos ... she left only 3 posts. Turns out she did that in the weeks leading up to her death.

Her family adds, "Niece was more than her struggles. She was beautiful and kind, sensitive and funny, creative and talented, generous and compassionate, thoughtful and challenging. While it is so very painful to say goodbye, we take comfort knowing she is reunited with her father, her three grandparents, her Uncle Rusty, and her beloved Puff; and that she is now free to be herself and, finally, at peace."

RIP