'Ms. Shirley' Raines Cause of Death Revealed

Shirley Raines -- also known as activist and founder of Beauty 2 The Streetz, "Ms. Shirley" -- passed away from hypertensive heart disease.

Shirley's daughter Danielle confirmed the news to TMZ ... telling us Shirley had a history of high blood pressure, which she was being treated for at the time of her passing.

A private service is scheduled for next Monday ... while a public one will be held at a later date.

As we told you ... Shirley was found unresponsive in her Nevada home late last month during a wellness check. She was later pronounced dead.

Raines rose to prominence after founding Beauty 2 The Streetz -- a non-profit that provides beauty and hygiene services to people living in the Skid Row area of Downtown Los Angeles

The rest of the team behind B2TS released a heartfelt statement in Shirley's honor after her passing ... saying, "Her legacy will continue to live on through the work she started and the hearts she touched."

Ms. Shirley was 58.