Ken Baker, executive news editor for E! News, told ABCNews.com that Johnson's life was not what it appeared. In August, Johnson and then girlfriend Semel approached Baker about doing a reality show on their lives as a Hollywood lesbian couple.
"How strange, I thought, she was this heiress from one of the wealthiest families and wanted to be a reality star," Baker said. "There was something incongruous about that. What she made clear to me was that she was basically on her own.
"She was ready to put her daughter and her life on TV," Baker said. "She wanted to make her own family and her own life. She just really wanted to create a family. She felt she didn't have that for whatever reason."
Baker believes Johnson was estranged from her wealthy family, including mom Nancy Sale Frey Johnson, who was divorced from her father, and may have been cut off financially.
But Grubman said Johnson "loved her mother dearly and her parents loved her very, very much. I can only imagine they are devastated."
On Monday, the Johnson family released a statement, The Associated Press reported, saying it's "mourning its tragic loss, and asks for privacy during this very difficult time."
It's been reported that Johnson's mother had been taking care of Ava for some time. Johnson reportedly struggled with drug and alcohol addiction, though Grubman said she never saw it. When Grubman had dinner with Johnson, her former intern, three months ago, she said Johnson was "very sober. She was in great shape."
But a few days later, Johnson, according to media reports, returned to rehab. "People were worried about her," Baker said. "More than one person over the last couple years told me they were worried about her."
One person who was worried was former friend Jasmine Lennard, a model and British reality TV star. "I tried to get her off drugs and alcohol. I tried to get her into a 12-step program. I tried to help take care of her daughter and gave her money. I am the only person who helped this girl," Lennard told the New York Post's Page Six.
On Tuesday, Lennard said in a statement to ABCNews.com, "Casey was a classy, witty, beautiful lady, whom I loved deeply. My thoughts go out to her family, who have suffered such a terrible loss. I am completely devastated."
Last year Lennard was ready to get a restraining order against Johnson, who she says broke into her Hollywood home and took $22,000 worth of jewelry, underwear and other items. Johnson was arrested and released on $20,000 bail.
"I believe she was obsessed with me and thinks in her mind we had some kind of affair," Lennard told Page Six at the time. "That is not the case. She breaks into my apartment, gets into my bed, has a shower in my bathroom, then takes everything. I've had a hell of a lot of patience and compassion for this woman and she just hasn't treated me right. Casey is an evil girl."
Instead of the fame she sought, Johnson attracted infamy. While they were dating, Semel and Johnson had a nasty fight that ended with Johnson's hair reportedly catching fire.
Another time, Johnson started a public feud with her aunt Libet Johnson, when she accused her of seducing her then 38-year-old boyfriend, music manager John Dee. "An old woman with a lot of money is a very powerful aphrodisiac," Johnson told Page Six.
"My impression is she felt that she could be as big as Paris Hilton," Baker said. "She was like the real Paris Hilton but wasn't as famous as her."