Danielle Spencer — famous for playing Dee Thomas on the hit ’70s sitcom “What’s Happening!!” — spent her final days alive in a hospital bed … she had tubes hooked up to her nose, and needed them for food and medicine.

Danielle’s mom, Cheryl Pelt, tells TMZ … Danielle was hospitalized August 1 after a urinary tract infection turned septic. She was unable to eat hard foods and had to get her nutrients and meds through tubing.

What’s more, we’re told Danielle had pneumonia in both lungs … and she was losing weight and her gastric cancer was kicking up.

The former child star’s mother says Danielle suffered a “code blue” and was unresponsive … doctors worked on her and found a pulse, and she was transferred to the ICU for more targeted treatment … but her heart was weakening.

As we reported, Danielle died Monday at 60 years old. Her mother says she died of cardiac arrest and gastric cancer.

Danielle’s mother says after her acting career slowed, she started working as a veterinarian in the Los Angeles area for over two decades … which was always her dream after acting.

But we’re told Danielle got sick in 2013 and she moved in with her mother at Cheryl’s home in Virginia …

Danielle’s mom says her daughter suffered a long time … she battled cancer, and there were long-lasting health complications from a severe car accident back in the day, which killed her stepfather, Tim Pelt.